68 Dairy Bacteriology. 



somewhat slimy. The curd usually diminishes in bulk, 

 due to the gradual digestion or peptonization of the casein 

 by proteid-dissolving enzyms (tryptic type) that are also 

 produced by the bacteria causing the change. 



A large number of bacteria possess the property of af- 

 fecting milk in the above way. Generally they are able 

 to liquefy gelatin (also a peptonizing process) and form 

 spores. The Tyrothrix type of bacteria (so named by Du- 

 claux on account of the supposed relation to cheese ripen- 

 ing) belongs to this class. The hay and potato forms are 

 also digesters. Organisms of this type are generally as- 

 sociated with filth and manure, and find their way into 

 the milk from the accumulations on the coat of the aniinal. 



Conn ' has separated the rennet enzym from bacterial 

 cultures in a relatively pure condition, while Fermi' 2 has 

 isolated the digestive principle from several species. 



Duclaux 3 has given to this digesting enzym the name 

 casease or cheese ferment. These isolated ferments when 

 added to fresh milk possess the power of causing the char- 

 acteristic curdling and subsequent digestion quite inde- 

 pendent of cell development. The quantity of ferment 

 produced by different species differs materially in some 

 cases. In these digestive fermentations, the chemical trans- 

 formations are profound, the complex proteid molecule 

 being broken down into albumoses, peptones, amido-acids 

 (ty rosin and leucin) and ammonia as well as fatty acids. 



Not infrequently these fermentations gain the ascend- 

 ency over the normal souring change, but under ordinary 

 conditions they are held in abeyance, although this type of 

 bacteria is always present to some extent in milk. When 



' Conn, 5 Kept, Storrs Expt. Stat.. 1892. p. 396. 

 Fermi, Arch. f. Hyg., 1892, 14:1. 

 * Duclaux, Le Lait, p. 121. 



