44 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
there will be a decided decrease in the number of bacteria 
for the first six hours after the milk is drawn from the 
cow; at 26 to 29° C. (79 to 84° F.) the decrease is less 
rapid, but continues for eight to ten hours, and at 15° C. 
(60° F.) itis still further reduced in rate but continues for 
about twenty-four hours (Rosenau and McCoy). The 
effect of the same milk on different species of bacteria is 
different, and the effect of different milks on the same 
species of bacteria also varies, showing that the antibodies 
are specific for certain species of bacteria. The germic- 
idal power of milk is not capable of destroying all bac- 
teria which may gain access to milk during milking and 
the subsequent handling; hence precautions against bac- 
terial contamination together with proper cooling are 
none the less necessary. It is also incapable of always 
preventing the development of pathogenic bacteria. 
These organisms may enter the teat canal and milk cistern 
and even invade the gland alveoli. Heating milk for 
thirty minutes to 56° C. (133° F.) considerably weakens 
the germicidal property, and it is entirely destroyed by a 
temperature of 70° C. (158° F.), or above, for thirty 
minutes. Bacteria, therefore, grow more rapidly in 
heated milk than in fresh raw milk. The germicidal 
power of colostrum and of milk from cows affected with 
mastitis is greater than that of normal milk. 
Toxins.—It has been demonstrated that tetanus toxin 
‘ may be eliminated in the milk of a cow affected with 
tetanus, and in sufficient quantity to kill mice fed with 
the milk (Miessner). There is, therefore, reason to be- 
lieve that other bacterial toxins are also eliminated in 
the milk, although there is no direct proof. However, 
the quantity of toxin circulating in the blood is very 
small, even in severely infected animals, and only a 
