196 ESSENTIALS OF BACTERIOLOGY 



Small-pox and Vaccinia. The exciting agent of small-pox 

 is still unknown, but numerous bacteria and protozoon-like 

 bodies have been described and given etiologic significance by 

 various authors. There is some evidence in favor of Funck's 

 belief that vaccinia is caused by a protozoon, the Sporidium 

 vaccinale. Animals inoculated with this organism developed 

 both vaccinia and variola. 



Yellow Fever. For some years it was thought that a bacil- 

 lus, called Bacillus icteroides by Sanarelli, was the cause of 

 yellow fever. The earlier work of Sternberg was disproved 

 when it was shown that his bacillus, Bacillus X, was identical 

 with the colon group, and Reed and Carroll found that San- 

 arelli 's germ was an allied organism. 



It is now known that a special species of mosquito, Stegomyia 

 fasciata, conveys the infection and acts as a culture-medium for 

 some unknown microorganism, possibly a protozoon, which 

 must undergo certain changes to become virulent. 



Only by the bite of a mosquito infected with the blood of a 

 yellow-fever patient or by direct inoculation of such blood can 

 yellow-fever be transmitted. 



The experiments made so far show that the germ is destroyed 

 by a temperature of 55 C. for ten minutes. It can pass 

 through a Berkefeld filter, and is, therefore, extremely minute, 

 but no one has as yet been able to find any distinctive organism 

 in any of the blood. 



CHAPTER XXI 



BACTERIA PATHOGENIC FOR ANIMALS BUT NOT FOR 



MAN 



A GREAT many bacteria have been described in diseases 

 peculiar to the lower animals which have only slight patho- 

 genicity for man, and only some of the more prominent 

 varieties can be treated of here. 



Bacillus of Symptomatic Anthrax (Bellinger and Feser) . 



