THE DAIRY 197 



curdles, and even putrefies, after Pasteurisation. A case of 

 this kind recently came under the writer's notice near Pretoria, 

 the injurious organisms being Bacillus subtilis and allied species. 

 The trouble arose from the very dusty condition of the kraals 

 in which the cows were milked, and after Pasteurisation the 

 milk did not keep as well as un-Pasteurised milk, becoming 

 curdled without the formation of acid. In this case the 

 destruction of the lactic organisms was apparently complete, 

 and in their absence the spores of Bacillus suhtUia multiplied 

 more rapidly than if they (the lactic organisms) had been 

 present, and thus led to the coagulation of the casein without 

 souring. In some cases the coagulum redissolved on further 

 standing, but the milk soon became repulsive in appearance 

 and flavour. 



Fortunately, as most of the pathogenic organisms likely to 

 occur in milk do not form spores, Pasteurised milk is generally 

 safe from risk of conveying contagion. 



The most satisfactory method of distingUL^ihing sterilised or 

 Pasteurised milk from fresh milk is by a determination of the 

 soluble albumin. In fresh milk this amounts to about 0*4 per 

 cent., while in milk heated to about 70° 0. only about 0*25 

 per cent, will remain, and if the milk be heated to 80° C. the 

 whole of the albumin is coagulated and precipitated. 



Fresh milk also contains an enzyme, which with para- 

 phenylene diamine, CgH4(NHj,)2, and hydrogen peroxide gives a 

 blue colour. In Pasteurised milk this enzyme is largely 

 destroyed, while in sterilised milk it is entirely absent. 



PpesePVation by Antiseptics. — By adding various sub- 

 stances to milk the growth of the micro-organisms can be 

 greatly impeded, so that the milk becomes sour much more 

 slowly. The amounts of the antiseptics added, however, can 

 never be suflicient to destroy pathogenic organisms, and thus 

 render milk safe from a hygienic standpoint. Moreover, it is 

 probable that the presence of antiseptics in milk renders it 

 less digestible. 



