59 



The filtrate showed no growth in bouillon, and yet when injected 

 into nonimmunes produced yellow fever. The blood from the latter 

 was also shown to be capable of producing yellow fever when injected 

 into a third subject. 



That the men inoculated with the filtrate suffered from yellow fever 

 induced by a morphologic entity which passed the filter, and not from 

 a toxemia, was shown not only by their rather long periods of incu- 

 bation, but was conclusively shown by carrying their experiment to 

 the third degree. 



The following experiments were planned in order to determine 

 among other things whether the organism of yellow fever, as it exists 

 in the blood serum, is capable of passing the pores of the Pasteur- 

 Chamber land B filter : 



An investigation of„the literature of the other filterable viruses 

 shows that the South African horse sickness is the only one which has 

 yet been reported as having passed the Chamberland B filter. 



In the filters of the Pasteur-Chamberland system those marked 

 " B " are finer, more compact, with thicker walls, and consequently 

 less porous than those marked F. We have been informed by 

 Assistant Surgeon-General H. D. Geddings, who has recently inquired 

 about this in Paris, that only two grades — B and F— are now being 

 made. 



The subjects used for our experimentation were all volunteers, non- 

 immunes, and carefully selected from among the native Mexicans at 

 Jalapa and the adjacent mountainous country, taken by train to Vera 

 Cruz, and immediately placed within the screened wards of our hos- 

 pital. All cases recovered. 



Jalapa is a town having an elevation of about 4,000 feet, where yel- 

 low fever has never been known to spread and has not existed, except 

 for the cases occasionally imported from the coast (tierra caliente). 



In order that the case from which we drew the blood for filtration , 

 should be one in which there was the highest degree of confidence as 

 to the diagnosis of yellow fever, we decided to produce the disease 

 through the bites of infected mosquitoes rather than to select a case 

 by clinical evidence alone from the yellow-fever wards. 



Mosquitos which had been allowed to feed upon typical cases of 

 yellow fever in San Sebastian Hospital, Vera Cruz, were applied in 

 succession to the hands of four persons whom we had selected as 

 being nonimmunes. The first three failed to become infected, but 

 the fourth took sick with what proved typical yellow fever. The 

 histories of the three negative cases are here given in brief : 



G. M., age 22, Mexican.— On August 13 he was taken to Vera Cruz 



and placed in our screened ward. August 15, at 3.20 p. m., he was 



bitten by two mosquitoes which had fed twelve days previously, at 



9.30 a. m., on J. R., a fatal case of yellow fever. Nothing unusual 



13046—05 M 3 



