196 



AGRICULTURAL BACTERIOLOGY. 



FlG. 24. 



shows large numbers that have the power of liquefying gelatin, 

 and, since these are quite sure to get into milk, it follows that 

 ordinary milk probably contains some of this enzyme-pro- 

 ducing class. They are so very common that they may be 

 regarded as normal dairy bacteria (Fig. 24,/). 



It is very doubtful whether this type of bacteria is of much, 

 or of any, significance in ordinary dairying. Although the 

 varieties are numerous and their number may be great at the 

 start, greater than that of the lactic bacteria, they very rarely 

 get an opportunity to have any considerable effect upon the 

 milk. The lactic bacteria grow so very much more rapidly 

 that they soon entirely outnumber the rennet-forming class, 

 and, indeed, in most cases stop their growth. As a re- 

 sult, whereas the latter may be com- 

 paratively numerous in fresh milk, 

 they become less, rather than more, 

 abundant as the lactic bacteria grow, 

 and finally disappear. Under such 

 conditions their significance in the 

 milk is probably nothing. Occasion- 

 ally, however, these bacteria may 

 become of more importance. It may 

 happen that a sample of milk does 

 not chance to have any lactic or- 

 ganisms in it, or that they are so few 



as to fail to get the upper hand of the others. If this occurs 

 the other species of bacteria may find the conditions favor- 

 able to their growth. A dairyman sometimes finds, especially 

 in the fall of the year, that his milk curdles without becoming 

 acid, an effect produced by the growth of this class of bacteria. 

 Some of the phenomena so troublesome in the dairy may be 

 attributed either to the great abundance of this second type of 

 bacteria or to a lack of a sufficient number of lactic bacteria to 

 counteract their action. It is a fact, also, that this class of 



A common milk bacillus pro- 

 ducing rennet and pepsin-like en- 

 zymes. 



