Methods of Determination of Pathogenic Microbes. 119 



realized : the nutritive media are, for the most part, 

 prepared empirically, starting from complex animal 

 or vegetable products, and not only are we unac- 

 quainted with the qualitative and quantitative com- 

 position of these media, but we are also ignorant of 

 the special nutritive value of the essential principles 

 they contain. Moreover, our culture apparatus are 

 very imperfect; during the progress of the culture 

 the nutritive material becomes exhausted and charged 

 with the products of nutrition, products which are 

 prejudicial to the normal life of the germs. From 

 tliese circumstances it results that artificial cultures 

 do not always give individuals conforming with 

 those which are sowed, and that often, in the case of 

 pathogenic species, they furnish degenerated beings 

 incapable of acting upon man or animals. 



Generally speaking, all culture media ought to 'con- 

 tain, besides the necessary nutritive substances, at 

 least sixty per cent of water, they should be neutral 

 or slightly alkaline, and absolutely sterile. A con- 

 siderable number of media are in use; they embrace 

 organic liquids : milk, urine, blood serum ; various 

 decoctions : bouillons of meat, hay, fruits, beer wort, 

 etc. These materials are used alone or after the ad- 

 dition of supplementary nutritive substances : pep- 

 tone, gelatin, glycerin, glucose, phosphates, etc. 



Without entering into the details of the prepara- 

 tion of these diverse media we will describe those 

 most commonly in use. 



