62 LABORATORY GUIDE IN BACTERIOLOGY 



nitrates, or from oxidation of ammonia. The ability of organisms 

 to produce these reactions is of great importance in their differ- 

 entiation. A control test with a tube of sterile medium should 

 be made. 



8. Enzym production: Proteolytic enzym 

 production noted by the liquefaction of 

 gelatin or casein. Coagulative, recognized 

 by precipitation of casein, if acid forma- 

 tion is absent, or present only in quantities 

 less than 0.4 per cent. Amylolytic, by 

 the digestion of starch (potato). 



9. Characteristic odor. 



10. Pathogenesis: What pathogenic effect has 

 the organism on man? What effect on 

 animals, and which animals? What dis- 

 eases are caused by the organism in man 

 or animal? 



Note. — The terms "proteolysis,'' "enzym production,'' and 

 "coagulation" are frequently confusing to the beginner. The 

 following brief explanation will aid in an intelligent interpretation 

 of the reactions observed. 



"Proteolysis" is the breaking up of complex nitrogenoiis 

 compounds (proteins), rendering them soluble. This process is 

 also expressed by the terms "peptonization" and "liquefaction." 

 The liquefaction of gelatin is one kind of proteolysis. Gelatin 

 is composed of nitrogenous matter (albuminoid or gelatinoid), 

 and it is for this reason mainly that gelatin stab cultures are 

 made. If the gelatin is liquefied, the assumption is that the 

 organism is capable of producing a "proteolytic" or gelatinolytic 

 enzym. In milk the process is more complex, and this medium, 

 on account of its composition (fat, milk sugar, casein, lactalbu- 

 min), offers excellent opportunities for the organism to develop 

 different characteristics. Milk is one of the most important of 

 media. The casein, contained in milk in colloid solution, may be 

 precipitated by an enzym or by an acid. This precipitate forms 

 the coagulum. At least 0.4 per cent of acid, which is largely 



