Delation of Disease-Bacteria to Milk. 91 



tubercle bacilli or not, still the interests of public health 

 demand that no milk from such stock be used for human 

 food until it has toen rendered safe by some satisfactory 

 treatment. 



1. Heating. By far the best treatment that can be given 

 such milk is to heat it. The temperature at which this 

 should be done depends upon the thermal death point of 

 the tubercle bacillus, a question concerning which there 

 has been conisderable difference of opinion until very re- 

 cently. According to the work of some of the earlier in- 

 vestigators, the tubercle bacillus in its vegetative stage is 

 endowed with powers of resistance greater than those pos- 

 sessed by any other pathogenic organism. This work has 

 not been substantiated loy the most recent investigations 

 on this subject. In determining the thermal death point 

 of this organism, as of any other, not only must the tern- 

 perature be considered, but the period of exposure as well, 

 and where that exposure is made in milk, another factor 

 must be considered, viz., the presence of conditions per- 

 mitting of the formation of a " scalded layer," for as Smith l 

 first pointed out, the resistance of the tubercle organism 

 toward heat is greatly increased under these conditions. 

 If tuberculous milk is heated in a closed receptacle where 

 this scalded membrane cannot be produced, the tubercle 

 bacillus is killed at 140 F. in 15 to 20 minutes. These 

 results which were first determined by Smith, under labora- 

 tory conditions, and confirmed by Russell and Hastings, 9 

 where tuberculous milk was heated in commercial pasteur- 

 izers, have also been verified by Hesse. 8 A great practical 

 advantage which accrues from the treatment of milk at 



1 Th. Smith. Journ. of Expt. Med., 1899, 4: 217. 



2 Russell and Hastings, 18 Rept. Wis. Expt. Stat., 1901. 

 8 Hesse, Zeit. f. Hyg., 1900, 34:346. 



