274 PATHOGENIC BACTERIA. 



ance. The existence of cholera organisms in milk is, 

 however, rather short-lived, for the occurrence of any 

 acidity at once destroys them. 



WolfFhugel and Riedel have shown that if the spirilla 

 are plunged in sterilized water they grow with great ra- 

 pidity after a short time, and can be found alive after 

 months have passed. Frankel points out that this ability 

 to grow and remain vital for long periods in sterilized 

 water does not guarantee the same power in unsterilized 

 water, for in the latter the simultaneous growth of other 

 bacteria in a few days serves to extinguish the cholera 

 germs. 



One of the characteristics of the cholera spirillum is 

 the metabolic production of indol. The detection of this 

 substance is easy if the spirilla are grown in a transparent 

 colorless solution. As the cholera organisms also produce 

 nitrites, all that is necessary is to add a drop or two of 

 chemically pure sulphuric acid to the culture-medium 

 for the production of the well-known reddish color. 



Several toxic products of the metabolism of the spirilla 

 have been isolated. Brieger and Frankel have isolated 

 a toxalbumin ; Villiers, a toxic alkaloid fatal to guinea- 

 pigs ; and Gamaleia, two substances about equally toxic. 



The cholera spirilla can be found with great constancy 

 in the intestinal evacuations of all cholera cases, and can 

 often be found in the drinking-water, milk, and upon 

 vegetables, etc. in cholera-infected districts. There can 

 be little doubt that they find their way into the body 

 through the food and drink. Many cases are reported 

 in the literature upon cholera that show how the disease- 

 germs enter the drinking-water, and are thus distributed ; 

 how they are sometimes thoughtlessly sprinkled over veg- 

 etables, offered for sale in the streets, with water from 

 polluted gutters ; how they enter milk with water used 

 to dilute it ; how they are carried about in clothing and 

 upon foodstuffs ; how they can be brought to articles of 

 food upon the table by flies which have preyed upon 

 cholera excrement ; and how many other interesting in- 



