9 



inferred that the parasite is one of those that requires for the complete 

 evolution of its life cycle a mammalian and an arthropod host. We 

 have familiar analogies in Piropla&mxi higeminum of Texas fever and 

 the Plasmodium of malaria. Because of these analogies it is inferred 

 that biologically it may be grouped! with them as a protozoon. On 

 the basis of these and other analogies, both Schaudinn (1904) and Novy 

 & Knapp (1906) have suggested that it may be a Spirochaeta. Stim- 

 son's recent discovery of a spirochsete-like organism in the tubules 

 of a yellow fever kidney is, therefore, exceedingly interesting and 

 suggestive. 



The cycle in man is represented clinically by a stage of incubation 

 and by a stage of fever. Some attempts to infect mosquitoes by allow- 

 ing them to bite subjects during the stage of incubation, in one instance 

 as late as 6 hours before the onset of the stage of fever, have been 

 unsuccessful; whereas a mosquito that bit a case of the disease 8 

 hours after the onset became infected and conveyed the disease to a 

 nonimmune' 26 days later. This would indicate that the parasite does 

 not appear in the circulating blood until the onset of the disease. We 

 already know that it remains in the blood only during the first three 

 days of the disease or, at least, it is only during those three days that 

 it exists in a form capable of continuing its life cycle in the mosquito 

 or in a fresh nonimmune. 



In the circulation it exists in a form so minute as to be capable of 

 passing through the finest grained porcelain filters, such as the Cfaam- 

 berland B and the Chamberland F. 



Its resistance to deleterious influences is feeble when withdrawn 

 from the circulation. When kept in a test tube exposed to the air in 

 the dark, at a temperature of 24° C. (75° F.) to 30° C. (80° F.), it 

 loses its virulence in 48 hours. Under the same conditions, but pro- 

 tected from the air by keeping under oil, it retains its vitality some- 

 what longer — up to between 5 and 8 days. Heating for 5 minutes 

 at 55° C. (132° F.) apparently suffices to kill it. The effect of low 

 temperatures has not been studied. 



The cycle in the mosquito requires at least 12 (?) days 01 for its com- 

 pletion. As to the changes which it undergoes during this period we 

 are in complete ignorance. 



The French commission has recorded one experiment which would 

 indicate that the parasite may,. under certain circumstances, be trans- 

 mitted to the progeny of an infected mosquito through the egg. An 

 attempt by Rosenau and Goldberger to confirm this resulted negatively. 

 The same commission attempted, but without success, to transmit the 

 parasite from one mosquito to another by feeding larvae with cadavers 

 of infected adults; they appear, however, to have succeeded in trans- 



. , . . » 



a See page 5, footnote e . 

 2742— No, 16—07 2 



