i MILK 127 



Finally, if the smell is unpleasant and there are numerous 

 gas bubbles present, then the milk is absolutely unfit for 

 human consumption or for dairy purposes. Often a elear layer 

 is to be seen below the cream, whilst the rest of the mass is 

 evenly coagulated. This is caused by the so-called peptonising 

 bacteria (principally hay bacteria), and is an indication that 

 these unwelcome guests are present in large numbers in the 

 milk. 



A. Peter, who has thoroughly investigated the fermentation 

 test, gives five types of fermentation, each divided into three 

 stages. He allows the fermentation to take place for longer 

 than twelve hours, namely, fifteen to twenty-four hours at 

 38-40. A synopsis of the different appearances which milk 

 may have after fermentation is given on the opposite page. 

 The table is based upon the original photographs taken by 

 Peter, and those portions which appear in ordinary type are to 

 be regarded as normal manifestations of fermentation, and not 

 to be due to impure milk. The sections printed in italics are 

 doubtful manifestations, whilst those in capitals indicate a 

 milk which is dangerous to consume or to use for making 

 cheese. 



When use is made of Peter's table it is possible to get good 

 comparative results, and use can be made of the contractions 

 used in the table when noting down the result. 



The fermentation test is used with much success in various 

 countries, particularly in Switzerland, for testing the milk 

 delivered to cheese factories to ascertain its suitability for 

 making into cheese. Its use could be extended to analytical 

 laboratories with advantage, for from this test a good notion is 

 obtained of the bacterial condition of the milk. Attention 

 must, however, be once more drawn to the necessity of 

 thoroughly cleaning, preferably also sterilising the test-tubes, 

 for without such precautions the results are worthless. 



THE REDUCTASE TEST. 



This test is based upon the feet first noticed by Duclaux l 

 that ordinary normal cow's milk has the power of converting 



1 Le Laif, t'tu<l<* fhtiiiiqiu* >t microbiologiques, Paris, 1887. 



