244 THE COAGULATION OF MILK. 



R. WARINGTON (II.) as well examined a number of such species,. 

 and observed that they all liquefy nutrient gelatin. 



The ratio between these two enzymes differs in the various- 

 species. A few produce the casein solvent alone, and when sown 

 in milk do not precipitate the casein, but decompose it direct into 

 soluble fission products, among which leucin and tyrosin have 

 already been identified. In proportion as the casein disappears 

 the milk becomes clearer, and is finally quite transparent. 



The production and activity of both these enzymes are variously 

 dependent on external influences, the one resembling lab being; 

 able to act only within narrow limits of temperature, whilst the- 

 other the proteolytic enzyme has a wider sphere of activity. 

 The same applies to the methods of nutrition of the bacteria in 

 question. A species examined on this point by Conn initially pro- 

 duced both enzymes, but subsequently after prolonged cultivation 

 on gelatin yielded the proteolytic one only ; and by increased 

 interference the production of the latter also can be restricted. 

 WOOD (I.) attained this object by adding, during several suc- 

 cessive generations, a little carbolic acid to the nutrient bouillon, 

 employed. 



The constitution of casease has not yet been accurately de- 

 termined, neither has any one succeeded in ascertaining whether,, 

 and in what respect, this enzyme differs from pepsin and trypsiri 

 which it greatly resembles in action nor whether the casein- 

 dissolving enzyme produced by different species of bacteria is the 

 same in all cases. WEJGMANN (VI.) states that he has isolated 

 casease from bacterial cultures, and that this substance favours 

 and accelerates ripening when added to fresh cheese. 



The spontaneous coagulation of milk without the co-operation 

 of micro-organisms, the possibility of which was maintained by 

 early workers, denied by Lister, and finally established as a fact 

 by Meissner, was more closely examined in 1887 by A. LEVY (I.), 

 who found that a very faint coagulation can be detected in all 

 milk that has been left to stand for some time. The sediment 

 deposited by such milk contains, however, only a small quantity 

 of coagulated casein, the bulk consisting of small fragments of de- 

 composed colostrum. As the cells of this latter substance die off 

 a slight degree of acidification ensues, which causes the precipita- 

 tion of a certain quantity of casein. 



The rapid curdling of milk so frequently observed during 

 thunderstorms has not yet been satisfactorily explained. The 

 opinion expressed by J. LIEBIG (I.) in 1890 will not bear investi- 

 gation, and the assumption put forward, on experimental grounds, 

 by G. TOLOMEI (I.), that it is caused by the action of ozone pro- 

 duced by electrical discharges, rests on insufficient foundation. 

 The same objection also applies to the views held by H. GERST- 

 MANN (I.) on this point. 



