Panama: antimalarial strategies



Drainage, which Colonel Gorgas puts as first in importance of the anti-mosquito measures, is carried out wherever possible; and indeed one sees it where at first sight it would appear to be of little benefit. On the swamps at the Atlantic side of the Isthmus, where the land and water are almost on the same level, drains have been cut often only nine inches or a foot deep. Yet, wherever it is possible to concentrate the water even in the slightest degree, it is done, for by so doing a great saving of oil is effected. If the water of a swamp can be reduced below the level of the surface of the ground for even only a few weeks in the year, much oil and labour are saved, and a dangerous breeding place is removed. As we have seen, Anopheles albimanus is, above all things, a lover of puddles and of the small isolated shallow pools which are so abundant where water stands almost at the ground level. Where the water level is high, every depression in the ground, however small, may at times represent a pool isolated from its neighbours, and seldom containing fish; and since in a swamp the ground is never absolutely level, at times many such breeding places may exist. So on the Isthmus one sees open drains varying from 6 inches deep and 2 feet wide, to great drains 20 feet wide and many feet deep, and every variety of channel which can convey water.


Open drains

These are really extensions of the rivers; and, as I have said, are of every size. The larger channels, drains, and rivers are not considered so dangerous as the smaller drains; for in wet weather, when the current is strong, all larvae are washed away. As will be found, too, from my visit to British Guiana, other conditions exist which make these channels quite harmless. The smaller drains, especially those on the hillsides, are also harmless in very wet weather; but the strong rush of water then erodes the banks, and makes potholes and depressions in bed; and so, although harmless in wet weather, they become dangerous breeding places in dry weather when each depression and pothole is an isolated pool. These drains are kept free from grass as far as possible, and are heavily oiled; but they require constant care, which means expense, and so they are being replaced by other forms of drains whenever practicable.

Open drains
Figure 11.1: Tile drains ending in an open drain cut in rock, at Gatun, Panama. Men seen in the middle distance of the photograph are relaying the pipes, which had been blocked by grass roots.

Tile Drainage

This was introduced by Mr Le Prince as early as 1906. The pipes are laid down in a true grade, and are covered by stone of about 4 to 6 inches in diameter. No earth is put over the stone. “The dirt from the trench must be placed on the downhill side of the line, to prevent it washing back into the ditch. When the soil uphill from the ditch is covered with vegetation, the space between the cover-stones does not fill up.”41 This form of drainage has been extensively used, and is being still laid down, as I saw at Gatun; but it is being gradually ousted as favourite by another and cheaper form of drain—the wire drain. The tile drain in Panama has given trouble in two ways. First, because having been covered by a stone that weathered easily and ultimately sealed up the joints, its effective life was only about four to six years; then the drain had to be reopened, and another kind of stone placed over it. Secondly, one of the grasses (cabaloté), when allowed to grow over the stones, found an entrance into the tiles, and blocked them with a mass of roots. In spite of these drawbacks, large areas have been effectually freed from Anopheles for many years by these pipes; and the Americans deserve great credit for the manner in which they have developed this important way of eliminating the Anopheles.


The Wire Drain

This was introduced by one of the sanitary inspectors, and, on account of its cheapness, it has been very extensively used in the past three years. It costs only 5 cents a foot against 20 cents for a tile drain, and so is displacing the latter. The wire drain is a shallow, open drain, made by putting down a length of wire netting and filling it in with concrete. Where the “seepage” is slight, the drain is only 6 inches wide. From this it varies up to a channel 2 or 3 feet wide “keyed” into the sides.

The tile drain as laid down in Panama would be useless in a ravine in the Federated Malay States, for the friable, sandy soil here would find its way between the stones on the top of the pipe in the first shower, and block it. This actually happened in Kuala Lumpur. That it is possible to maintain a wire drain in steep ravines and hillsides in Panama, shows the difference between the soil there and that in the Federated Malay States. In Kuala Lumpur an open cement drain, except at quite a low grade, was found to be useless; for the rate of soil erosion was so great, that after a few showers the open drain was left standing above the ground level, while the stream it was built to carry flowed cheerfully outside.

I wish to insist strongly on the importance of considering the nature of the soil before deciding on the form of drainage. To follow the system of putting large stones on top of the pipes, as is done in Panama, may in other countries mean failure. It was a failure, although not the sole cause of the failure to control malaria, in Kuala Lumpur. On the other hand, having thought out a system of subsoil drainage after having read Howard’s Malaria Prophylaxis in Small Communities in British Central Africa, in 1907, and before I had heard of what had been done in Panama, I escaped the danger. In Howard’s thoughtful account of the malaria of these places in Central Africa, he describes how mosquitoes breed in the streams and along the shore of the sandy island of Likoma, near the eastern shore of Lake Nyassa:

In the neighbourhood of the lake there are streams which rise as springs in the sand, with a dry watercourse above. They are quite short for the most part, about 100 yards long, and they do not begin to flow until the rainy season has been established a month or so. If the rains come early they may be found running in December, in other years not till February. The actual course of the stream is variable; a sudden rush of rain water will cut quite a new channel through the beach to the lake. A heavy storm brings down quantities of sand which, meeting the waves of the lake, is thrown up as a bar at the mouth of each stream, behind which the water collects as a pond. With every heavy rain the water cuts through this bar and reaches the lake, but during a few consecutive fine days the ordinary flow of the stream escapes by soaking through the sand.

Early in the rainy season fish make their way up the streams to spawn, so that the ponds and streams are soon full of young fry. These effectually destroy Anopheline larvae, and at the beginning of the wet season the latter are only found where they are out of reach of the fish. Such places, however, are only too plentiful. Reeds or grass may grow in the course of the stream and so give shelter, or some slight obstruction may cause an eddy which during a rainstorm scoops out a pool in the sand. As the water subsides, the pool is left securely shut off from the main stream, which contains fish, and is kept fresh by the soakage through the sand of the water running close to it. Such pools form ideal breeding places, and are often crowded with larvae.

At first sight, the destruction of Anopheline breeding places in an island like Likoma might appear easy, but in practice the uncertain course of the streams through the sand, and the rise and fall of the lake, make it impracticable. Even if regular brick drains were made, it would be quite likely that the rush of water, bringing down tons of sand from above, would block them up, and cut a new channel for itself. Moreover, the cost of such a scheme would be prohibitive, for lime cannot be procured less than 100 miles away, and costs £6 per ton, while cement from England costs nearly £17 per ton. Lastly, owing to the quantity of sand which the water brings down, coupled with the annual rise and fall of the lake, it is impossible to prevent the formation of a bar with the pond behind it at the mouth of such stream.

The Wire Drain
Figure 11.2: An open cement channel in the Federated Malay States, which had to be replaced by a subsoil pipe in the steeper portion of the ravine because of the soil erosion. Such a channel as this could be put down anywhere in the Canal Zone without any such risk.

Reading over this account, and wondering how the pools in the streams could be abolished, it struck me that a pipe buried in the ground with grass allowed to grow over it to stop erosion, was the solution of the difficulty; and that if cement and kerosene were high-priced commodities there, clay certainly would be cheap, and the manufacture of tile pipes present no great difficulty. And so, when I thought of using tile pipes for the first time, it was for an island in Central Africa, not for the Federated Malay States; but in September 1908, after the matter had been discussed with Mr J. Scott-Mason, late acting Governor of British North Borneo, then chairman of the Klang Sanitary Board, and with Mr John Gibson, the general manager of the Tremelbye Rubber Company, Limited, some pipes were made for the Board by Mr Low Joy of Klang. They were not laid down, however, as Mr Simm’s paper in the Annals of Tropical Medicine and Hygiene showed the Americans had employed tile drains in Panama for well over a year before the idea had even occurred to me.

Later still, in 1909, when I had come to the conclusion that our hill land differed radically from the flat land, and would never become healthy like the flat land through cultivation, I reverted to the idea of the tile drain; but I insisted the pipes should be laid down according to my original method, and not as was done in Panama. And so from the first, on estates in the Federated Malay States, the pipes have been buried in the earth and no stones have been placed over them.

I have thought it necessary to go into this matter, because it serves to emphasise the supreme importance of every man in charge of anti-malaria work thinking out every detail for himself, and weighing carefully the local conditions. Merely to copy faithfully what is a success in another place does not by any means guarantee success.

Although drainage has been extensively carried out and has been of great value, it seems to me to be quite secondary in importance to oiling on most of the zone. When it has been possible to lay down a permanent drainage system, as has been the case in a few places, e.g. in part of Gatun, mosquito breeding places have been permanently abolished, and oiling is unnecessary. No other measure directed against the mosquito and against malaria is so simple and permanent as drainage; and hence Colonel Gorgas places it first in order of importance,42 and Mr Le Prince says: “Drainage and eradication of breeding areas is the all-important work in an anti-malarial campaign.”43 But it seems to me the supreme merit of the Panama work that, not being in a position to apply the best method which at one stroke would have given success, they have yet achieved almost complete success by a combination of other and inferior methods, which have required the highest degree of organization and infinite care, not for a day or a month, but for over a whole decade. Their position has been as if they had a wild beast by the throat, but were not allowed to kill it; yet, if for a moment they relaxed their grip, the beast would be on them.

I have shown how at a number of stations, e.g. Ancon, Matachin, Culebra, etc., drainage systems have been destroyed by “dumping.” In some stations breeding places could not be drained for want of “fall;” in others nothing permanent has been laid down, because the place would be abandoned on completion of the Canal; and in others, new breeding places were constantly being made. And so, for one reason or another, the Sanitary Department have not been in a position to construct what they desired—a permanent drainage system—but have been compelled to leave the breeding places and kill the larvae in them every week—truly a Sisyphean task.

To have, by oiling, to eradicate malaria over an area of 50 square miles of country, where the water appeared in every conceivable form, in springs, in pools, in rivers; and bottomless swamps, was a task which would have daunted all but men confident in the scientific basis of their practice and determined to succeed. Colonel Gorgas did not hesitate, and at once proceeded to build up an oiling system which would give the best results at the minimum cost; for throughout economy has been considered as carefully as efficiency.

To reduce the handling of oil to a minimum, the Sanitary Department has tanks at many stations connected with the trans-isthmian pipeline. Pipes are also laid on the places which require much oil, or where carriage presents special difficulties, as in the bottom of the cut. In some places mules carry oil to the men; in other places an oil cart sprays oil onto the roadside ditches; oil drips from barrels on to the streams; and cotton waste, soaked in oil and anchored in springs, gives off a constant film. When swamps are deep and extensive, boats fitted with sprayers spread the oil.



Table 11.1: Cost of oiling and larvicide use in the Panama Canal zone in March 1913
Item   Cost Sum
larvicide spreading labour $1395.00  
  material (8910 gallons ) $1556.00  
Oil spreading labour $1584.93  
  material (50,441 gallons) $1297.41  
Total     $5833.34

In every way the number of labourers is reduced. At one station I found 35 gallons of material (a mixture of oil and larvicide) had been spread in half a day by four men, who were supplied with the oil by three men carrying it from the depot. That is, it costs seven dollars in labour to spray one dollar’s worth of material. This is much above the average for the whole zone; but it shows how important it was to economise labour. The actual figures for March, 1913, for the whole zone are listed in Table 11.1. The total cost of unskilled labour, material, and supplies on the Canal zone in 1911–12 is given in Table 11.2. It amounts to $116 per square mile, or 18 cents per acre per month.

In Panama, crude oil, used also as fuel for engines, costs only $1.10 (gold) for a barrel containing 42 gallons. In the Federated Malay States the price has, in the last few years, risen to three times what it is in Panama.



The machine used in Panama is the Meyer’s Knapsack Sprayer. From the photograph in Figure 10.11 it will be seen that a long lever projects over and above the man, and this is pulled down by means of a rope to put the sprayer into action. It is easier to work this pump than those, like the “Vermorel,” where the handle is on the side of the pump, and is moved by a downward push of the hand.


Drip Barrels

The commonest form of this is a 30-gallon galvanised iron ash can,44 into the side of which an opening about 2 inches wide and 3/8 of an inch in height is made. “Into this opening is soldered a flat spout 13/4 inches wide, 1/4 inch high, 21/2 inches long, into which is inserted an ordinary wick,” such as is used in a spirit lamp. The rate of flow is regulated by compressing the spout until the oil drips with sufficient rapidity to give a good oil film. “The heavy oil used by us has a tendency to clog the wick. The clogging, is to a certain extent, prevented by putting into the bottom of the can sufficient water to reach within an inch or so of the wick. This water acts as a settling basin for impurities heavier than oil. In addition it is often necessary to ‘cut’ the oil by the addition of from 5 to 10 percent of the larvicide.”

Table 11.2: Cost of labour and supplies for sanitary work in the Canal Zone, in 1911–12
Item Cost
Labour, silver employees $79,499.19
Material and supplies $53,185.11
Total $132,684.30

“In order to be efficient, the drip can must be placed 2 or 3 feet above the surface of the water to which the drip is to be applied, so that the drops may strike the surface of the water with sufficient force to be broken up.” All the barrels in a district are numbered and shown on the Sanitary Department’s plan. One man is employed to keep them filled; and the inspector must see them each week. On some stations the drip is regulated by a screw; but it is doubtful if this is as efficient as the wick.



As the Sanitary Department found no larvicide was reliable, and all were very expensive, the manufacture of a good larvicide was begun at Ancon, in a shed connected by rail with the main line.

The details of the manufacture were worked out by Mr J. E. Jacob, chemist, Board of Health Laboratory. The work has been described as follows:45

In the work of destroying algae and mosquito larvae in the Canal zone, large quantities of the larvicide are used, the amount averaging 250 barrels a month, and a plant erected for its manufacture has been in operation for two years.46

The larvicide is prepared from crude carbolic acid, a substance which as usually applied contains from 5 percent to 10 percent tar acids, together with a large amount of inert neutral oils. The crude acid is immiscible with water, and is a very inefficient disinfectant on account of its inability to come into intimate contact with microorganisms. When, however, the crude carbolic acid is made into a liquid soap with rosin and alkali by means of heat, a product results which emulsifies upon the addition of a large amount of water. If the germicidal value of the emulsion is determined by the method of Rideal and Walker it will be found to be greatly enhanced, frequently being from two to five times greater than that of pure carbolic acid.

The product is not only a most effective destructive agent for mosquito larvae, but is a valuable and cheap disinfectant.

Method of manufacture: To ensure the manufacture of a uniform product, requisitions call for crude carbolic acid of a specific gravity not greater than 0.97, and to contain not less than 15 percent of tar acids. Each consignment of crude carbolic acid received is assayed at the laboratory to determine its specific gravity and percentage of tar acids, for it is necessary to keep the product of a specific gravity approximately that of water, so that it will diffuse rapidly, and neither sink to the bottom nor remain on the surface.

One hundred and fifty gallons of crude carbolic acid are heated in an iron tank, having a steam coil with steam at 50 lbs. pressure. Two hundred pounds of finely crushed and sifted common rosin are dissolved in the heated acid, and then 30 lbs. of caustic soda dissolved in 6 gallons of water are added. There is a mechanical stirring rod attached to the tank. The product is ready in a few minutes, yielding about 31/2 barrels.

The cost of manufacture, as given in the same reference, is listed in Table 11.3.

On mixing the larvicide with water it forms a white mixture something like Jeyes’ fluid. In a dilution of 1 in 5000 all larvae will be killed in five minutes, and 1 in 8000 will kill them in thirty minutes. The larvicide also kills algae on which the larvae feed, and is also destructive to other vegetable matter. The decomposition set up by this dead matter causes a pellicle to form on water, and thus further makes the water unfit for mosquitoes, even after the larvicide has itself disappeared.

The larvicide is used as a disinfectant for all sorts of things in the zone, e.g. privies, as well as to destroy larvae in water. It is also a very convenient preparation, because it does not burn the hands unless employed in full strength, and then for a long period.

It has, however, two very serious limitations: one is, that it loses its efficiency when exposed to the air for more than a hour; the other is, that it is ineffective in sea or brackish water. To prevent deterioration it is kept in a tightly closed container. “Larvicide shipped in barrels should not be kept longer in them than necessary,” says the Sanitary Inspector s Manual. The inspectors are also warned that “larvicide is an expensive product, and should be used in sufficient, but not in excessive quantities.”

Table 11.3: Cost of larvicide manufacture, August 1909. The total amount manufactures was 14,600 gallons (292 barrels).
Item Amount Price Extended Price
Carbolic acid, crude 12,600 gallons 12 cents/gallon $1,512.00
Rosin 12,300 lbs. $2.48/100 lbs. $305.04
Caustic soda 2,550 lbs. $3.70/100 lbs. $ 94.35
Coal 2 tons $5/ton $10.00
Labour     $92.46
Supervision     $50.00
Total     $2,063.85


Screened houses are much used in the United States. In New Orleans the best houses had a portion of the verandah screened, and had frames fixed to all windows, so that even when the glass frame was thrown up the house remained mosquito-proof. In Panama the Americans invented quite a new style of mosquito-proof dwelling. It is so new that the skill of the architect has not yet had time to relieve it of an uncompromising, almost puritanical plainness, which is accentuated by the outside colour scheme being a dismal drab or slate. All the houses are simply rectangular boxes, with some partitions inside to form the rooms, and screening over the whole of the verandahs. The boxes are made in many sizes, but the shape never varies. Some contain one family; others are so divided that two families live upstairs and two downstairs. The higher officials have larger houses still; but each and all are of the same design, and all are built of wood. All are provided with water supplies, bathrooms, and water-closets. The kitchens are inside the houses; not separate, as is the custom in the East.

Figure 11.3: Screened houses in Panama. A: Houses for four families at Corozal. B: House occupied by the Sanitary Inspector at Frijoles.

The wire gauze used to screen the houses is made of pure copper and zinc, for it is found that the admixture of even 1 percent of iron materially shortens the life of the gauze. It is obtained from three firms: The Clinton Wire Cloth Company, New York; the New Jersey Wire Cloth Company, New Jersey; and the W. S. Tyler Company, Cleveland, Ohio. Eighteen strands to the inch is the mesh used on the zone. When it shows signs of gathering dust, water is sprayed on to it from a hose.

None of the houses have “rotan chicks,” nor did I notice any kind of sunblind. To protect a house the gauze is applied to the outside of the verandah, or where there is no verandah it covers the window. Both on the verandahs and windows the gauze is fixed, and there are no openings into the house except doors. Doors open outwards; and it is not considered necessary to use double doors. By making the door open outwards, any mosquito which happens to be sitting on the door when it is opened is thrown outwards; were the door to open inwards, it is probable the mosquito would pass into the house in front of the person opening the door. The screening of all houses is regularly inspected and repaired if necessary.

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Figure 11.4: Screened railway wagons on the Panama Railroad used as dwelling-houses.

As so much is made by some critics of the difficulty of keeping screening intact, I specially noted the condition of the screening on the zone. On only three occasions did I observe damage. The worst damage was at Ancon Post Office, where the screening on the doors had large holes in it. This is a busy office, and the screening obviously required more than the usual protection of wooden spars if it was to stand. At Colon I noted damage to the door of one store and one dwelling house. I was told that the negro and Spanish employees often damage it in the most malicious way; but if so, it is promptly repaired. I wish to state very emphatically, and as the result of careful examination of houses during my stay on the zone, that the screening is maintained in good order, and in my opinion no one should have any difficulty in repeating what has been done in Panama with any class of labour, if he takes an interest in it. It is, however, of the greatest importance to get a material which, being free from iron, will not rust.

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Figure 11.5: Ancon Hospital, Panama. Built by the French. A: One of the wards, now screened. B: A house converted to screend quarters.

It is sometimes stated, as another objection to screened houses and hospitals, that they are mosquito traps: that mosquitoes get in and cannot get out again. It is certainly true that some mosquitoes find their way into screened houses; but the number that does is very small indeed compared with those that find their way into unscreened buildings. The fact that screened houses are a trap cannot be denied; but there is a silver lining to the cloud; for most of the mosquitoes that enter will be found in the early morning on the screening, where it is easy to catch and kill them in a wide-mouthed bottle containing a plug of cotton-wool soaked in chloroform or tobacco juice. Even if the mosquitoes are not so killed, their life in the house will last only a few days unless they get water. It has been observed that mosquitoes in a screened house during the day make for flower vases, sinks, and other collections of water, without which they soon die. On the advantage of trapping and killing Anopheles which may have bitten malaria patients in hospital, over allowing them to fly free every morning only to reinfect the patient again in the evening, or to infect the healthy inhabitants of the neighbourhood, it is unnecessary to speak. The value of screening is here overwhelming.

Although all Commission quarters were screened when the Americans first settled on the zone, by 1909 it was realized that screening was not so important as it had been; and circular No. 420, issued by the chief sanitary inspector on the 13th August of that year, marks in a very definite way the change of opinion. That circular stated that no new screening was to be put onto “married silver quarters;” nor was that already in existence to be repaired. The reason for this order was as follows: The Canal zone not being a colony where both men and women are wanted, the Commission, although anxious to attract labour in 1905, were not willing to spend much on accommodation for women, and in fact provided accommodation for only a comparatively few married negroes. It was sufficient, however, for the requirements; for in 1906 the zone had still a bad name, and did not attract married labour.

But with the marked improvement in health in 1907, negro labour came in freely, and the women began to come with their husbands. By 1908 the zone, from its high rate of pay, was very popular; and there now being married couples far in excess of the accommodation provided by the Commission, the negroes either hired houses, which were springing up on the outskirts of the stations, or built huts (“shacks”) for themselves. As these privately built houses or “shacks” were not screened, the Sanitary Department protected the occupants from malaria by extending the area treated with oil. So it came about that, instead of oiling and draining for only 200 yards round houses, the Department found it had to extend its operations for half a mile round each station, which was the situation when I paid my visit. When it was seen that the married labourers and their children in unscreened houses kept free from malaria, it was decided to stop screening the Commission quarters occupied by married negroes, that is, the “silver married quarters.”

Although Colonel Gorgas says:47 “Personally I lay great stress on screening. I would have it done always in the tropics. In early work, before mosquitoes are destroyed, screening is a great help. We are never sure enough of the disappearance of the mosquitoes to do away with screening. It is much preferable to live in screened houses than to be constantly taking prophylactic or malarial treatment. Of course, there will always be cases of malaria now and then, even in the best protected places.”

Although even now all quarters except those occupied by the “silver married” employees are screened, the freedom from malaria of the non-employees and of the employees who lived in unscreened houses, shows clearly that by 1909 the oiling and drainage carried out on the zone were in themselves sufficient to control the disease and reduce its incidence to a negligible quantity. So far as I can learn, the total number of those who, on 30th June, 1912, lived in screened quarters on the area controlled by the Sanitary Department was only 15 percent (see Table 11.4).

Table 11.4: Number of Canal Zone residents living in screened houses as of June 30th, 1912. The total population was 146,510.
Americans 8,908
Europeans 5,558
West Indians 8,915
Total 23,381


When the Sanitary Department first began work, it employed seventeen quinine dispensers, who visited the various squads of negroes at work and offered it to the men. The drug was also given gratis to all who applied for it at the dispensaries, and it was placed on all the hotel and mess tables. No attempt to compel people to take it was ever made. In 1909, Mr Le Prince estimates, “about half of our force gets a prophylactic dose of quinine each day.” But by 1913 I found that very few indeed took the drug except when actually ill with fever; and only two quinine dispensers were employed. It was clear that the good health of the zone did not depend on the inhabitants taking quinine.