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. ) it is 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 germie- 

 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. (133F.) 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 



