Panama: local malaria research


The Board of Health Laboratories

In a small, quite unpretentious building, Dr Darling carries on his multifarious duties and researches. I have already told how his laboratory devised the effective and relatively cheap larvicide which is so extensively used on the zone; I do not propose to dilate on the widespread usefulness of his laboratory, which examines anything from throat swabs for diphtheria to gear grease for engines. Fireclay and malignant tumours are equally sent for examination; while a considerable embalming business is carried on, for the bodies of all citizens of the United States who die on the zone are sent back to the place they came from. Apart from all this work, which, although routine, is of the highest value to the community, Dr Darling has found time to carry on research work on a number of important subjects. His discovery of the ease with which kittens can be infected with amoebic dysentery has gone far towards determining the relationship between the various bodies seen in a dysentery stool.63 Nor, in view of the serious nature of sleeping sickness, is his paper on the immunization of animals against a trypanosome disease any less interesting.64 Other papers deal with the oriental sore in Panama,65 relapsing fever,66 sarcosporidiosis,67 and show what good use is made of the wealth of material which pours into the laboratory at Ancon.

Into a volume entitled Studies in relation to Malaria, published at Washington by the Government Printing Office (1910), Dr Darling has collected a series of valuable observations on:

  • Anophelines of this region
  • Collection of larvae
  • Breeding out mosquitoes, and methods of feeding
  • Biting—infecting experiments
  • Estimation of gametes
  • Care of mosquitoes after feeding
  • Method of examining for zygotes and sporozoites
  • Description of the malaria parasite in the mosquito
  • Table of infecting experiments
  • Motes and conclusions from table of infecting experiments
  • Limit of infectiousness of man
  • Notes on the bionomics of Anophelines
  • Effect of salt or sea water on larvae
  • Experiments with larvicides
  • Experiments with agents destructive of vegetation grass, and algae
  • Experiments with screening of various mesh
  • Relative value of wire-screening of various composition, based on practical tests and chemical analyses
  • Notes on the value of the practice of killing Anophelines found in quarters and barracks
  • Latent malaria
  • Effect of quinine upon the parasite in mosquito and man

I have already had occasion to quote from Dr Darling’s researches on many of these points, so it is unnecessary to do more than mention them, but to several other points in this original paper I must refer.


Feeding Mosquitoes

All those who have attempted experimental work with mosquitoes know the difficulty there is in keeping the larvae, and especially the adults alive, in captivity. Dr Darling has ingeniously overcome some of these difficulties. He found that aerating the water with a “Pacquelin cautery bulb, having a heavy glass perforated tip,” kept the water fresh, and the larvae usually hatched out. The tanks are aerated with the fine jets of air twice a day. Dr Darling also found that adult mosquitoes could be kept alive on dates and raisins, along with a little water, and that this food suited the insect better than the usual banana, which seemed to induce the growth of yeasts and fermentative acids in the mosquito’s stomach, with fatal results.

Especially interesting were his experiments to determine how many of the gametes (male and female malaria parasites) failed to breed when taken up by the mosquito. To do this he weighed a number of mosquitoes before and after feeding, and determined that the average meal of blood weighed approximately 0.0008 gramme—its own weight in blood. He then counted the number of malaria parasites in a certain quantity of blood, and so determined the number the mosquito had sucked in. The experiment showed that no less than 97 percent of the parasites were lost—apparently another instance of the extreme prodigality of nature where sexual reproduction is concerned. And yet we need not be surprised at this in malaria, when we consider how few seeds ever become trees.


The malaria-carrying mosquitoes

After a series of experiments on mosquitoes, Dr Darling reached the conclusions that A. albimanus is the chief carrier of malaria on the zone. His results are shown in Table 14.1.

Table 14.1: Malaria-carrying Anopheles species. Results of infection experiments by Dr Darling.
Species Number Infected % Infected
A. malefactor 17
A. pseudopunctipennis 31 4 12.9
A. albimanus 48 34 70.2
A. argyritarsis1 4
A. tarsimaculata 5 3 60.0
A naturally infected specimen of this species has been found in barracks.

In view of the fact that the zygotes of malaria have been found in the stomach of such an Anopheles as A. rossii, this table cannot perhaps be taken as proving that A. pseudopunctipennis is a carrier of malaria when wild, and Dr Darling says it “is only slightly concerned in the transmission of malaria fever, if at all, not only from the fact that only four out of thirty-one mosquitoes under the most favourable artificial conditions became infected, but from the additional fact that relatively few specimens are taken in quarters at this time.”

A. malefactor, which is “widely distributed and abundant locally … active in entering houses, and a vigorous biter,”68 is shown by Dr Darling not to carry malaria. This is another warning not to assume an Anopheles is responsible for causing malaria in a place merely because it is abundant and freely feeds on man.


Human carriers of malaria

In March 1909 Dr Darling examined the blood of 269 Spanish labourers, part of whom lived at Ancon and part at Cucaracha. Twenty-nine, or fully 10 percent were found to have malaria in their blood. All the labourers had been at work, and were working every day. Later on two entered hospital with malaria, and it was noted that the two were not among those in whom malaria had been found. These labourers lived in screened houses. Among children and adults living in unscreened quarters the percentage infected was much higher; in one group four out of six, and in another six out of thirteen were infected. Dr Darling thus confirms what has been found in other countries, namely, that much malaria exists in a latent form during the period when people are acquiring immunity to the disease.



I have already described how on many occasions I found fish in the same water as larvae; and I am by no means certain to what extent they destroy larvae under natural conditions. Laboratory experiments are quite useless; for, as Dr Darling told me, he had put larvae into vessels containing various kinds of fish, and on every occasion except one the larvae were eaten up in a few hours. In the single exception, all the fish died in twenty-four hours, so it is probable they were not healthy. Not only are fish destructive of larvae when in bottles, but so are almost all the aquatic insects, such as water-beetles and dragonfly larvae. Many and many a time I have lost all the larvae I had spent hours in collecting by overlooking a diminutive aquatic insect. Yet it is obvious, from the great number of these enemies which one finds in water containing larvae, that they cannot possibly be so destructive when at large as when in a bottle; presumably the larvae are then unable to take cover.


Treatment of the sick

The treatment of the sick is carried out under the supervision of Colonel Mason. Originally there were ten hospitals on the Canal zone; but as early as 1907 this number was reduced to two large ones, situated at Colon and Ancon; there is also a very small one at Culebra, mainly for non-employees. This, of course, raised the efficiency of the hospitals, and also lowered the cost. In addition to the hospitals there have always been sick camps. These do not differ from the quarters in which the labour force is housed. They do not pretend to be hospitals, nor are they elaborately equipped like the hospitals, and the cost of running them is only forty-four cents per capita per day, against $1.21 for hospitals (these are the figures for 1911). How important a part these simple sick camps have played in the zone will be gathered from a glance at Table 14.2, which shows the admissions during the years 1907 to 1913 to the hospitals and camps, respectively.

Table 14.2: Annual admissions to hospitals and sick camps in the Canal zone
No. admitted 1907 1908 1909 1910 1911 1912 1913
To hospitals 32,063 27,251 27,154 32,239 34,196 32,129 30,993
To sick camps 32,451 27,528 18,102 19,991 18,296 12,333 1,208

It is important to note this point, for a moment’s consideration will show how greatly these sick camps must have reduced the total cost of treating the sick. In 1913 these camps were abolished, with the exception of a few at stations not on the railway, because the hospitals were, from the greatly diminished sick-rate on the zone, then able to accommodate all who could not be treated in their own homes or at the dispensaries. The year 1913 is distinguished as being that in which for the first time the Americans succeeded in completely abolishing the annual malarial wave, which is responsible for the filling of the hospitals at a certain period of the year.

In addition to the hospitals and sick camps, there are dispensaries under the district physicians. At these large numbers are treated. In 1912 there were 601,742 attendances. At the dispensaries the physician decides whether the patient is to be sent to hospital, to sick camp, or to be treated in his quarters—the local expression being “excused for quarters.” Of the hospitals I do not propose to say much, except that they are among the best in the tropics; and, as far as the work done in them is concerned, will take second place to none, whether within or out of the tropics. Many of the buildings are a legacy from the French. At Ancon they are scattered all round the hill; at Colon they are also isolated pavilions, but there they are built over the sea on the coral rocks. Like other Commission buildings they are screened. The nursing staff for both whites and blacks is white.

Dr Herrick is in charge of the surgical side of the hospital; Dr Deeks, of the medical; Dr W. M. James in charge of the clinical laboratory. Many valuable papers have been published from the wards of Ancon hospital on malaria, dysentery, and other diseases of the tropics, but I single out the volume on Haemoglobinuric Fever in the Canal Zone as an illuminating contribution to one of the most obscure problems of tropical medicine. Here, as well as later on I shall quote extensively from it, for the author’s words cannot be improved upon. It is based on a study of 224 cases, of whom 24 were Americans, 143 Europeans, 28 Barbadians, 23 West Indians, and 4 Panamanians, Chileans, or Mexicans.

After a most careful study of these cases, they arrive at certain conclusions which I give below; I would draw attention especially to No. 4. At this time when quinine has been dethroned from the high place upon which Koch placed it, there is a tendency among the public to fly to the opposite extreme and to say quinine is of no value. I am glad, therefore, that much emphasis has been placed on the neglect of quinine as a definite condition in the production of blackwater fever.

There is no proof that blackwater fever has spread from one country to another, or from one part of a country to another, as have kala-azar, yellow fever, and sleeping sickness. On the contrary, the disease invariably manifests itself when certain conditions relative to the epidemiology of malaria, and to that of no other disease, are present. These conditions are:

  1. (1)The presence of a population non-immune to malaria.
  2. (2)The prevalence of malaria in such quantity as to produce an almost continuous infection in this population.
  3. (3)A large proportion of estivo-autumnal malaria, because the amount of blackwater fever is in direct proportion to the intensity of this variety.
  4. (4)The neglect of prompt and continuous administration of quinine, especially in primary attacks, to persons nonimmune to malaria. In every locality, without exception, where these conditions obtain haemoglobinuric fever is found …

The primary cause in haemoglobinuric fever is either prior or coincident malaria, or both; the immediate cause is sometimes the administration of quinine, but this never acts unless the primary cause has been or is present. With this knowledge we are able to treat the syndrome intelligently, and often to prevent its occurrence by the removal of the primary cause, and by sending away from the source of infection those who, since by reason of personal idiosyncrasy they cannot take quinine at any time without the production of blackwater fever, should not remain in a malarious country.


Canal Zone Medical Association

After dinner one evening, Dr Darling introduced me to the Canal Zone Medical Association, of which Dr W. M. James was president. The meeting was well attended, another strong evidence of the keenness of the medical men on the zone. Dr Deeks, chief of the Medical Clinic, Ancon Hospital, read a paper on the clinical diagnosis and post-mortem findings of the last 500 consecutive fatal cases from his wards. The paper was profoundly interesting. It dealt with the different groups of diseases; gave the percentage of correct diagnoses in each group, where partly correct and where wrong, and discussed the various pitfalls for the diagnostician.

Despite all difficulties, Dr Deeks could point to over 80 percent of successes; to a considerable percentage where the difference was more in the name than anything else, and in the balance a correct diagnosis would have given the patient no better chance of life even if it could have been possible to make it during life. The discussion which followed was most interesting; and not least so were some of the different opinions as to how death should be classified, when malaria parasites, found in the wards, had disappeared under treatment, while at the autopsy no parasites or anything very definite could be found. When asked to speak, I congratulated the author on his paper and on his work, and said it reminded me of how Sir W. T. Gairdner studied his fatal cases in the post-mortem room.

The great physician learns in the post-mortem room no less than in the ward, and his patients reap the benefit in more correct diagnosis and more appropriate treatment. In conclusion, I would add that the Canal Zone Medical Association publishes its proceedings, to some of which I shall have occasion to refer later. For a moment I will refer to the kind but embarrassing way in which I was welcomed to this society, and also to one in Washington. Immediately after the minutes were read, and under the heading of “General,” the president referred in very kind terms to my presence, and asked me to tell them something about my work on malaria in Malaya. Luckily, my previous experience at Washington put me on my guard, and I produced a tabloid lecture on malaria lasting about ninety seconds. It was a kind welcome; but for those who are not aware of the custom, a somewhat embarrassing one, and I write this as a warning for any of my countrymen who have not yet visited the U.S.A.