CAUSING ACUTE INFECTIONS. 83 



called pyocyanin, soluble in chloroform:; the other is 

 a fluorescent pigment soluble in water. In old cul- 

 tures a ferment-like substance is formed called pyo- 

 cyanase, which has the property of dissolving some of 

 the other forms of bacteria. It has been used to 

 destroy diphtheria bacilli that persist in the throat 

 after recovery. The toxins formed by the bacillus are 

 both endo- and extra- cellular. Immunity in animals 

 is produced with much difficulty, but in man no- way 

 of producing immunity has been devised. 



THE SPIRILLUM OF ASIATIC CHOLERA. 



The micro-organism causing cholera is a small, 

 curved rod, often shaped like a comma, and therefore 

 called the comma bacillus. When two are placed end 

 to end they are S-shaped. True corkscrew forms 

 occur, particularly in cultures in fluid media. The 

 spirillum was discovered by Professor Koch in 1884. 

 It is motile, being propelled by a single flagellum 

 placed at one end, and grows on all the laboratory 

 media in the presence of oxygen. No spores are 

 formed. 



Cholera exists constantly in India and countries 



' tion of 



of the Orient. It has been carried occasionally to the dig ease 

 other countries, causing epidemics, A very bad epi- 

 demic occurred in Hamburg in 1892. In this country 

 the disease has been imported on several occasions, 

 but no epidemic has developed since 1873. Strict 

 measures are taken at the chief ports, New York, 



