CASEASE 187 



of casease. The same observer also discovered, in the case of several 

 species of Tyrothrix isolated from Cantal cheese, and of which a description will 

 be found in chapter xxxi., certain bacteria gifted with the faculty of excreting 

 both enzymes, the casein precipitant and the casein solvent. 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 \ as 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 successive generations, a little carbolic acid to the nutrient 

 bouillon employed. 



The constitution of casease has not yet been accurately determined, neither 

 has any one succeeded in ascertaining whether, and in what respect, this enzyme 

 differs from pepsin and trypsin which it greatly resembles in action nor 

 whether the casein-dissolving enzyme produced by different species of bacteria 

 is the same in all cases. WEIGMANN (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 decomposed colostrum. As the 

 cells of this latter substance die off a slight degree of acidification ensues, which 

 causes the precipitation of a certain quantity of casein. 



The rapid curdling of milk so frequently observed during thunder-storms has 

 not yet been satisfactorily explained. The opinion expressed by J. LIEBIG (I.) 

 in 1890 will not bear investigation, and the assumption put forward, on 

 experimental grounds, by G. TOLOMEI (I.), that it is caused by the action of 

 ozone produced by electrical discharges, rests on insufficient foundation. The 

 same objection also applies to the views held by H. GERSTMANN (I.) on this 

 point. 



