IMMUNIZATION EXPERIMENTS 251 



"(10) Experiments in the endeavor to transmit the fever by other mosquitoes 

 than Stegomyia fasciata have uniformly given negative results.* It is very 

 probable that the yellow fever virus is adapted to the organization of this single 

 species to the exclusion of all other culicids. 



" Were this not so, a biological phenomenon which is observed with most of 

 the species, the death of the female after the first egg-laying, would prevent the 

 virus absorbed by the individuals of these species, after piercing a patient, from 

 having the time to develop in their bodies in such a way as to render them 

 infectious. t 



"(11) Stegomyia fasciata escapes this rule. It is because the female is 

 capable of laying several successive batches of eggs that she acts as the inter- 

 mediary host of the fever. If she were to die regularly after her first laying, as 

 do so many other female Culicidse, yellow fever would be unknown.^' 



Conclusion No. 8, which reads, " The virus of yellow fever can be artificially 

 transmitted from mosquito to mosquito," and the conclusion following it, indi- 

 cating that this method of transmission is possible only under laboratory con- 

 ditions, needs further explanation to those not familiar with the original paper. 



A number of unsuccessful experiments in the transmission of yellow fever to 

 monkeys and other animals were tried in the search for an inoculation serum, 

 and for this purpose they carried 124 infected mosquitoes to France, 57 arriving 

 in living condition in Paris. They caused the mosquitoes to puncture an orang- 

 utan and a young chimpanzee, bringing about some elevation of temperature, 

 but they were unable to determine that this was due to a yellow-fever infection. 

 After having given periodically abundant injections of virulent human blood to 

 a horse, and finding diflBculties in the way of preparing an active serum which 

 would not be dangerous, they attempted to cultivate a serum in the mosquito. 

 They considered that if the germ which causes yellow fever issues from the mos- 

 quito in the form in which it enters it, it was a legitimate hope that a direct 

 transmission from one mosquito to another might be secured. They took living 

 mosquitoes, infected the 12th of February, 1904, pulverized them with glucose 

 added to a little physiological water. This mixture, rapidly prepared on the 10th 

 of March, was immediately offered to a certain number of young Aedes calopus 

 which had fasted for two days. The insects immediately took this nourishment. 

 Sixteen days later, the 26th of March, three of these mosquitoes bit a man. The 

 same individual was bitten by two more of these mosquitoes on the 28th. The 

 7th of April the patient felt uneasy ; the 8th he had a chill with pain in the limbs 

 and in the lumbar region; the thermometer, after having shown 39° the 8th of 

 April, 39.8° the 9th of April, returned to the normal on the 11th, On the 13th 

 there was a slight jaundice, with albumen in the urine — in fact, the man had 

 shown a clear case of yellow fever. The virus had then passed from one mos- 

 quito to another. The experimenters considered the significance of this experi- 

 ment as considerable, and believed that nothing would be easier than to procure 

 the virus in abundance in this way. They continued the work, starting with a 



• The species experimented with in this way were Cvlex quinquefasciatns, Aedes scapularis, 

 Aedes tCBniorhynchus, Psorophora posticatus, and Psorophora ciliata. — H., D. & K. 



t The French investigators still adhered to the belief that most mosquitoes deposit all their 

 eggs at once. We now know that a large proportion of mosquitoes lay their eggs in incomplete 

 batches at intervals and that, therefore, the yellow fever mosquito is by no means exceptional in 

 this respect. — H., D. & K. 



