Principles of Milk Preservation. 117 



is efficiently pasteurized. The kinds that are destroyed 

 are mainly the lactic acid species; those that resist the 

 pasteurizing heat are generally of the enzyme-forming 

 class, which in many cases are also able to liquefy gelatin. 

 The acidity of pasteurized products always increases some- 

 what, but even when it is curdled, it rarely contains over 

 0.3-0.4 % of acid. The organisms that remain belong 

 then to the sweet curdling type of bacteria. 



While these organisms capable of resisting the pasteur- 

 izing temperature are fermentative germs, it is also im- 

 portant to determine if they have the power of forming 

 toxic substances that exert a harmful effect on the ani- 

 mal body. Fluegge 1 has found several forms. in sterilized 

 milk that are able to produce highly toxic substances. 

 A similar study has been made under the writer's direc- 

 tion on the bacteria isolated in pasteurized milk under 

 commercial conditions. Shockley 2 studied thirteen differ- 

 ent forms found in pasteurized milk, but all of them with 

 a single exception failed to cause any disturbance when 

 inoculated into white mice and rabbits. In the single 

 instance, fatal results were only obtained when large 

 quantities were inoculated. 



1 Fluegge, Zeit. f. Hyg., 17: 272, 1894. 



2 Shockley, Thesis, Univ. of Wis., 1896. 



