28 THE REPORT OF THE No. 19 



After having established the fnct of the transmission of the disease through the agency of 

 mosquitoes, further investigations were carried on by the members of the commission in order 

 to discover if possible, the micro organism which caused it. Repeated experiments revealed 

 that the disease could be conveyed not only by the bite of the mosquito but also by the 

 injection of the blood serum of a yellow fever patient into the system of one who was not 

 previously immune to the infection. And this blood serum it was found could actually be 

 filtered through porcelain and jet still retain its power to convey the disease. On being 

 submitted to various degrees of heat, it was disc )vered that the sertjm lost its toxicity at a 

 comp;iratively low temperature, one too low to have effect upon any known toxin. It seems, 

 therefore, to be conclusively established that the cause of yellnw-fever is a micro-organism in 

 the blood which it is bej'ond the power of the microscope to detect. 



These experiments satisfactory as they were, did not entirely convince the physicians < f 

 the south, and accordingly othtr and independent investigations were made. In 1901 the 

 Havana Board of Health caused a series of experiments to be carried on at Lis Animas 

 Hospital under Dr. Guiteras, a well known yell>w-fever expert, and Dr. J. W. Ross the 

 director of the hospital. In a number oi cases the disease was conveyed by the bites of infected 

 mosquitoes and several of the pati-nts unhappily lost their lives, while those who submitted to 

 contact with infected clothing and at the s^me time were protected from mosquito bitts, came 

 out ot the ordeal in good health and perfectly free from the di-ease. These experiments were 

 conducted with the utmost care in order to preclude any doubt as to the certainity of their 

 results. They entirely corroborated the conclusions drawn by Dr. Reed from his investigations 

 of the previous year. 



Later on further experiments of a most careful kind were conducted at Sao Paulo, Brazil, 

 by Dr. Lutz, director of the Bacteriological Institution of that province. In this case mosqui- 

 toes were brought from uninfected places at a distance, allowed to bite a yellow fever patient, 

 and then conveyed to another uninfected region some hundreds of miles away ; there they 

 were allowed to bite nonimmunes who had been for some time quarantined and who volun- 

 tarily submitted to be ex peri me i ted upon. Ouc of six cases three contracted the disease, and 

 all happily recovered. The effect on public opinion of this experiment w^ very great, and all 

 opposition to the adoption of practical measures for the extermination of mosquitoes was soon 

 abandoned. 



If further proof of the reality and importance of this discovery were needed, it may be 

 found in the fact that now the City of Havana is free, and has been so for many months, from 

 the plague of yellow fever — for the first time probably in its history. That this immuni'y is 

 not due to other causes is evident from the fact that although the city was th 'roughly cleansed * 

 and effective sanitary measures were put in operation during the America-i administration and 

 under the Cuban Board of Health, yellow fever still prevailed while the general health in other 

 respects was vastly improved. When, however, the extermination of mosquitoes was under- 

 taken, their breeding places destroyed, and all yellow fever patients protected from the bites 

 of these insects, the dissemination of the disease was at once checked and no fresh cases 

 occurred. This was indeed a great scientific triumph — one that has brought immense blessings 

 in its train, and which has opened the way to future achievements for the benefit of mankind 

 in various regions of medical investigation. 



Dr Howard gave a description of the mosquito, Stegomyia fasciata, and stated that it was 

 in the habit of biting in the day time as well as at night ; that it was essentially a house insect, 

 breedin,' in water tanks and barrels, in the roof troughs, and anywhere where standing water 

 was to be found ; it was not usually met with in the woods, but was very abundant in cities 

 and towns. Its thorax, abdomen and legs are banded with white, and hence it is named 

 fasciatn, the striped mosquito, (Fig. 2); the larva resembles that of other mosquitoes, and being 



