FERMENTS IN MILK. 49 
are so effective in producing unfavorable conditions, these should 
be chiefly employed in controlling the growth of micro- 
organisms in the dairy industry. 
Kind of Germs Found in Milk.—The number of species of 
germs found in milk has not. yet been definitely established, 
due chiefly to the fact that it is in some instances difficult 
Fic. 8—Shows a plate exposed in pasture where air must have been very 
pure and free from germs, (Bul. 87, Nebraska.) 
for bacteriologists to differentiate one species from another. 
The description of one species of bacteria by two different bac- 
teriologists may vary considerably, as the characteristics of 
the germs depend so much upon the conditions throughout 
the classification process. Over 200 different species have 
been described. It is possible, however, though all of these 
types may have different morphological and physiological 
characteristics as described by different bacteriologists, that 
some two or more of the 200 types may belong to one species. 
