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criticising my former experiences, to consider a fact which they have 

 themselves demonstrated, namely, that there are two different ways by 

 which the specific germs of yellow fever may be conveyed from the sick to 

 the healthy. One way consists, as I infer from their experiments, in allowing 

 the yellow fever mosquito to become infected in such a manner that, after 

 the lapse of a certain number of days, the salivary and venom glands of the 

 insect appear to become the seat of a local, chronic, lifelpng infection, 

 which is attended with a constant reproduction of yellow fever germs, so 

 that the contaminated mosquito will thereafter inoculate some of those 

 germs contained in the blood of a yellow fever patient directly under the 

 skin of a non-immune. I am not aware that any attempts have been made 

 to determine the length of time during which the specific germs in the 

 blood may retain their vitality within the glass cylinder of the hypodermic 

 syringe or in any other receptacle, ty but it stands to reason that they 

 will survive more readily within the blood-sucking apparatus of the yellow 

 fever mosquito, normally moistened with the insect's saliva, which 

 admittedly constitutes the ideal culture medium for the yellow fever germ. 

 Yet there must be a time limit beyond which the germs retained within the 

 sucking apparatus must lose their vitality or perhaps undergo 

 transformations which may temporarily deprive them of the power of 

 reproducing the disease. During that limited time, under favorable 

 circumstances, they may even sporulate and multiply as they might have 

 done within the human host, but, on the other hand, it must be 

 remembered that their position in the internal mouthpieces of the insect 

 must be a precarious one, being at every moment liable to be washed out by 

 a discharge of saliva or to be drawn into the stomach of the mosquito 

 whenever food or water is sucked. 



From these considerations it must be inferred that the bite of a yellow 

 fever mosquito which has sucked the blood of a severe case is likely to 

 prove infectious for non-immunes at two separate periods, namely, during 

 the first few days after the insect has bitten the patient, provided that, 

 in the meantime, the mosquito has not had access to any food or water, nor 

 been allowed to bite another subject. After this short period the bite of the 

 insect may be harmless until ten or fifteen days later, when the germs 

 within the body of the insect will have had time to multiply and to invade 

 its salivary apparatus. 



The direct infection through the bite of recently contaminated 

 mosquitoes, so far as I can judge from personal experience, produces much 

 milder pathogenic effects, the fever is much less prone to develop albumin- 

 uria, and the period of incubation is often prolonged. I believe that after 



1) Since writing the above, I have been informed of a recent experiment by 

 Dr. Carrol!, at Camp Columbia, showing that the blood of a mild experimental case of 

 yellow fever, kept over night and part of the next day (some 14 hours) and injected 

 to a non-immune has produced a mild but characteristic attack of the disease. 



