Pasteurisation, 59 



be expected. It was, therefore, surmised that full milk 

 would stand heating to 107 equally well without ac- 

 quiring the boiled taste, and experiments have con- 

 firmed this supposition. The keeping quality of a: 

 milk pasteurized at 167 was enhanced by twenty- 

 four to twenty-eight hours if the storing temperature 

 w r as 73, and sixty hours if the temperature of stor- 

 age was GO , and was also enhanced in the same 

 measure as by a pasteurization at 155 lasting thirty 

 minutes. 



The investigations of Prof. H. L. Russell, of more 

 recent date, have thrown a great deal of light on the 

 effect of pasteurizing on the different species of bac- 

 teria in milk. P^xcluding from consideration those 

 species that have occurred only sporadically in the 

 cultures of bacteria, fifteen different forms in all have 

 been isolated from normal milk and cream. Of this 

 number, six different forms have predominated in a 

 large degree. When classified as to their effect on 

 milk they are grouped as follo\vs : 



Species producing lactic acid 3 



Species causing no apparent change in milk: 7 



Species coagulating milk by the production of rennet and 



subsequently digesting the curdled casein 5 



Iii the same milk, after pasteurizing, only six 

 species were isolated. Of these, three had no ap- 

 parent action on milk, while the remaining three 

 species curdled the milk by the formation of rennet 

 and then subsequently digested the same by the ac- 



