malaria in 5 mainland and 3 island countries of the Caribbean Sea during a period 3 years had not revealed a single case, although over 65,000 persons were examined. However, the surveys made in the Chagres River Basin in connection with our malarial work accidentally brought to light a number of cases of infection with T. cruzi, the trypanosomal parasite causing Chagas' disease. Up to the present time, 19 cases in humans have been recorded with three deaths attributed to this disease. The deaths occurred in children from 3 months to 3 years of age.

Of the 110 vampire bats which have been studied, 5 were found to have a natural infection of T. cruzi. Observations on these will be reported later on. We have been able to infect bats experimentally with Chagas' disease, and also with the local form of relapsing fever, but we have so far failed in attempts to pass either of these diseases from the infected bats to other animals.

DEPARTMENT OF HELMINTHOLOGY

The study of Strongylus vulgaris is under the direction of Dr. A. O. Foster, staff helminthologist. We believe that this parasitic worm is probably responsible for more general loss of efficiency in horses and mules than any other single factor in and about the Isthmus. Almost without fail this parasite causes some degree of injury to the mesenteric arterial tree and sometimes to the aorta as well. As a rule it is the adult stage of an intestinal parasite that causes the injury to its host, but in this case it is the larval stage that produces the serious lesion. One can treat with fair success the adult stage of this worm, but we have had no success with any treatment for the larvae. Injuries to the artery may occur either as a result of thrombo-arteritis with encroachment on the lumen or a large aneurysmal development with mural thrombosis and perhaps embolism. It has been our belief that yearlings and 2-year olds are the most seriously affected and that animals that survive this period, in many cases, are left with an artery or small aneurysm that does not seriously disturb function. In our study of a series of colts from the day of birth to about 6 months of age, we have been astounded to learn that four out of seven, ranging in age from 1 to 7 days, had a thrombo-arteritis almost occluding the lumen of the vessel and in one instance showing several small larvae. This indicates prenatal infection and certainly makes any effort to control the spread of this parasite far more difficult. Our investigations will proceed with the hope that we can invite cooperative studies by others and eventually find some way of controlling this dangerous parasite. This is a problem of the temperate zones as well as the Tropics. Dr. Foster is making an extensive survey of all equine worms in various parts of Panama as well as in imported animals. Comparative records on range and stabled animals are also being accumulated.

PROBLEMS ENGAGING THE PERSONNEL ON TOUR OF DUTY

W. H. W. Komp, sanitary engineer, United States Public Health Service, entered a cooperative service with our laboratory on April 1, 1931, and he is still actively engaged in anopheline mosquito studies and in all work pertaining to the Santa Rosa station. During the past year the observations on malaria incidence and the experiments

in malaria control through treatment of the "human seed bed" have been continued. In addition to the five villages grouped around the Santa Rosa station, a sixth group of natives having their dwellings along the Madden Dam Highway about 5 miles from our river towns have been included in the surveys as a control with which to compare results in the river towns. The inhabitants of all six localities have been surveyed each month, specimens of blood being taken and examined for malarial parasites. All the individuals in the first four villages whose blood was found to contain parasites were treated with atebrin and plasmochin. Those in the fifth town were given quinine and plasmochin so that the relative effectiveness of the atebrin and quinine might be determined. The treatment in these six villages was carefully supervised by members of the laboratory staff with the assistance of native nurses. The control group on the Madden Dam Highway was surveyed in the same manner but no attempt was made to supervise the treatment. A list of those found parasite-positive was posted and quinine was made available for the use of all who applied for it but the inhabitants were left to follow. their own ideas as to the taking of our advice and treatment. This provided an opportunity to check the value of our supervised treatment with a group where very little quinine was taken.

When the first surveys were made in 1929, the combined parasite rate of all the villages was about 62 percent. By October 1934 malaria rates in all villages had fallen to a low level, usually below 10 percent, and we felt that by a process of education and better administration of drugs we had reduced the "seed bed" to such an extent that an epidemic of malaria in the area under observation was not likely to However, at the completion of the Madden Dam, new conditions developed which increased mosquito breeding in the vicinity of our villages, and during December 1934 and January and February 1935 the parasite rate jumped to an average of 30 percent. The rate remained high in all the towns over a period of 4 months in spite of intensive treatment. There was also a noticeable increase in the number of clinical cases (sick), a good many suffering from fever and a number being confined to bed. The sick rate, however, was under thoroughly good control and there were no deaths.

The rate in our control group on the Madden Dam Highway rose at the same time but to only a slightly higher percentage than in the towns under supervised treatment. When the epidemic began to decline in our treated towns in April and May 1935 the rates in the control group also declined, although no change had been made in the manner of administering treatment there.

It is important to note that during the period when we experienced the epidemic in our villages, there was a sharp rise in the malaria rates in the rigidly sanitated Canal Zone where mosquito proofing of houses and general antimosquito measures have been in practice for 32 years. In view of the failure of drug treatment to prevent such a sharply defined epidemic in towns which had been under intensive antimalaria treatment for more than 3 years, we have been forced to conclude that under the conditions obtaining in our Panama River villages, the theoretically sound and economically feasible plan of malaria control by attacking the "seed bed" of infection in young children and adolescents, was not successful in practice. Although we were able to reduce the amount of clinical malaria and get the

sufferers to their feet again by the use of atebrin and plasmochin, we were unable to prevent new infections or cut down the number of relapses in those already infected. We are led to believe that equally good results in controlling clinical malaria might be accomplished by the employment of a native "practicante" who would visit the villages every few days and administer antimalaria treatment to anyone with fever, without the use of the expensive and time-consuming monthly blood surveys in use in the past.

As a byproduct of the malaria-control experiments, much valuable information has been secured concerning the course of epidemics of malaria which will be of great service to others enaged in similar work. We have also demonstrated the presence of "malaria families", whose members are much more susceptible to malaria than the general population. There exists also the opposite condition in certain families, who are apparently malaria-proof to a high degree.

The fifth report on drug control of malaria in these river villages has been prepared for presentation before the National Malaria Committee meeting in St. Louis, in November.

During the first part of June 1935, at the invitation of the medical department of the Standard Oil Co. of New Jersey, Sanitary Engineer W. W. Komp made a malaria and mosquito survey of the Caripito division of the Standard Oil Co. of Venezuela, in eastern Venezuela. He discovered the presence there of Anopheles darlingi, undoubtedly one of the most dangerous malaria-carrying mosquitoes of South America, and gave information regarding its control. He also instructed the hospital laboratory force in the thick-film technique of malaria diagnosis, and made several blood surveys which proved the usefulness of the prophylactic measures then in force against malaria infection. His mosquito survey, although necessarily incomplete, showed the presence of over 40 species, some of which are extremely important from the standpoint of yellow fever, as they have been found capable of transmitting the virus of this disease.

Mr. Komp spent July, August, and September 1935 at the invitation of the Rockefeller Foundation, in making a mosquito survey of an endemic focus of yellow fever in the interior of the Republic of Colombia, South America. The identity of the mosquito suspected on epidemiological grounds was established, the breeding place of another mosquito whose relationship to the well-known "yellow fever mosquito" is very close, was discovered, and the life histories of many other species was worked out. Over 75 distinct species of mosquitoes were found, including many hitherto unknown larvae and males, and at least three species entirely new to science were discovered. The work done during the 3 months will form the basis of an extensive report on the mosquitoes of the region in relation to yellow-fever transmission.

Lt. Col. H. S. Eakins, of the Veterinary Corps of the United States Army joined us in October 1931 and remained until July 1935. No immediate steps are to be taken to replace him. He has been in charge of our Miraflores Veterinary Station during this period of time. His chief problem was a survey of the Canal Zone, Army, and Republic of Panama equine stock for trypanosomiasis and the direction of treatment of animals found positive for the disease. As a result of his work, this disease cannot be found at present in the Canal Zone and neighboring parts of the Republic. The index was

also greatly reduced in the Provinces of Cocle, Herrera, and Los Santos where the disease is endemic in the vast unfenced ranges of that region. He acted as a consultant on various problems connected with the raising of domestic animals and pursued studies on osteomalacia. The Gorgas Memorial Laboratory and the Republic of Panama have derived great benefit from his tour of duty with us.

Lt. Comdr. E. G. Hakansson, of the Medical Corps of the United States Navy and two technicians, J. F. Buckner and H. A. Down, are on tour of duty with us engaged in research work. Dr. Hakansson came to us May 19, 1934. (Refer to our list of publications for 1935 for the contributions made by his unit.) During the first 3 months of their service, this unit assisted our protozoologist in making a survey for amoebic infections in the patients and staff of Retiro Matias Hernandez, an asylum of the Republic of Panama situated about 13 miles east of Panama City. More than 3,000 stools were examined and the results have been recorded and tabulated to constitute a basis for studies on the epidemiology of amoebiasis and the various clinical features of the disease. Coincident with this survey, observations were made on the morpology of the human protozoa and a particular study was made of the use of aqueous smears. It was found that some interesting morphological features were revealed during the process of distention and disintegration of the protozoa in the water, and that some of these characteristics were of value in the differentiation of the species. These findings have been published in the American Journal of Tropical Medicine, volume 15, no. 4, page 439. During the early part of 1935, considerable work was done on the viability of the cysts of E. histolytica. The findings of these investigations are to be checked before publication. The major problem during the last 6 months has dealt with the efficacy of amebacides, particularly Carbarsone. A series of cases have been treated and others are under treatment. A method of check-up has been worked out that we believe will determine beyond a reasonable doubt whether or not a cure has been effected. The final results of this work will not be recorded before the end of the calendar year. A study of the Dientamoeba fragilis and its clinical significance is also being made. Cases in which D. fragilis infections have caused gastrointestinal disturbances have been observed and these will be reported

soon.

VISITING SCIENTISTS

Drs. W. H. Taliaferro and Lucy G. Taliaferro with an assistant, Mrs. Cessa Kluver, spent the months of March, April, and May conducting further research in regard to monkey malaria and the blood and blood-forming organs. They returned to the University of Chicago with abundant material to continue their investigations. This staff has completed many excellent pieces of work on this subject as our previous reports will indicate. A publication will soon be made by them on the cellular reactions against P. brasilianum in monkeys.

Samuel F. Hildebrand, senior ichthyologist, Bureau of Fisheries, Washington, D. C., arrived January 26, 1935, and left March 11, 1935. He spent this period of time in studying conditions in Gatun Lake with the idea in mind of finding a species of fish, such as perhaps the carp, which might feed on the plant life that is so abundant

in certain arms of this lake where massive breeding grounds for anopheline mosquitoes exist. It was also hoped that additional surfacefeeding minnows might be introduced to help in the control of mosquito larvae and pupae. He reached the conclusion that native predatory life in the lake would not let the carp reach a desired abundance. He also feels that the predatory minnows we now have as surface feeders would probably defeat any efforts to introduce other species. A second feature of Dr. Hildebrand's work was to offer us scientific identification of our food fishes, since we have under consideration a study of the parasites in the meat and blood of these fishes.

Advantage was taken also of the opportunity to make a fish census of all fresh and salt waters in and near the Isthmus, and added to this was a thorough study of the stranded fish in the dewatered Gatun locks that were undergoing cleaning and repair at the time. The margins of Gatun and Miraflores Lakes were also included. He found no evidence of salt water fishes being reared in these lakes although many large specimens of tarpon, jack, bonyfish, snook, and snappers were present in addition to many small species of salt water life. Many of these large fishes were full of mature eggs and males were found with milt. This indicates that these impounded sea fishes can live in the lake but that either their eggs are destroyed in the lakes when spawned or, what is more likely, they escape through the locks and go to sea to spawn.

He also visited the Chiriqui Viejo River, where some years ago he helped introduce trout. This introduction has been a great success. Dr. Hildebrand's final studies may not all appear soon in detail, since he has enough material collected to consume a lot of time in recording all of it. We have received from his office a list of fishes from 13 locations that includes 29 families and 97 species. This gives us an excellent start in our studies of fish parasites for it will enable us to check the fish under study against the scientifically identified specimens. (See our list of publications for Dr. Hildebrand's report on the rainbow trout of Chiriqui.)

PROGRESS NOTES ON SNAKE CENSUS

We have shipped (Oct. 1, 1935) to the Museum of Comparative Zoology at Harvard, as our present year's catch, 849 snakes, of which 157 represented poisonous snakes of 7 species. We received two specimens from the high trout level of the Chiriqui Viejo River caught by a fisherman (Earl Pfeifer) as he climbed out of the river. One of these, Bothrops nigroviridis nigroviridis, is a prehensile bush or tree snake that has never been recorded for Panama. The second was also a bush snake, Bothrops lateralis and only one specimen of it has ever been taken in Panama. Both of these are poisonous snakes. Our collections have all been confined to the lowlands of Panama and we have little information on the tablelands and mountains. Our shipment of snake collections from January 1, 1929, to September 30, 1935, now totals 4,306 snakes, of which 993 (23.06 percent) were venomous and divided among the following species: