450 AGEICULTUBAL AND INDUSTRIAL B ACTEKIOLOGT 



Udder Infection. — It has previously been stated that 

 the normal healthy tissues of animals usually do not eon- 

 tain living bacteria. This is true of the tissues of the mam- 

 mary gland. However, there are apparently some bacteria 

 which find conditions favorable for development in the milk 

 cistern and in the larger duets of the udder. The number 

 found here differs greatly with different individuals, some 

 animals normally having large numbers, others compar- 

 atively small numbers or even none. It is apparent, there- 

 fore, that the milk first drawn from the udder usually will 

 contain somewhat larger numbers of bacteria than that 

 drawn later. Very rarely do the numbers of bacteria 

 amount to more than 100 per cubic centimeter in the freshly 

 drawn milk. Animals revealing larger numbers usually are 

 suffering from some udder infection. 



Bacteria from Body Surfaces. — When animals are 

 milked by hand into an open pail, it is inevitable that 

 particles of dust and dirt adhering to the skin and hair will 

 fall into the milk. Usually these are covered with large 

 numbers of bacteria. If the animal is filthy, the numbers 

 gaining access to the milk in this way may be considerable. 

 Under usual conditions, however, the proportion of bacteria 

 gaining access in this manner is not so large as from some 

 other sources. It should be noted that this source of bac- 

 teria is very largely avoided in the use of the milking 

 machine. 



Bacteria from the Dust. — If the air in the stable or barn 

 in which the cows are being milked is filled with dust, some 

 will, of course, gain access to the milk and add to the num- 

 bers of bacteria present. Unless conditions are very bad, 

 however, the total number of bacteria gaining access in this 

 manner is not sufficient to be notable. This source of infec- 

 tion is also, in part at least, guarded against by properly 

 constructed milking machines. The organisms gaining 



