PREVENTIVE MEDICINE 233 



In raw milk they were found to be alive (Gasperini) for 10 days, at 

 the end of which they were probably destroyed by lactic acid. 

 Harrison found them to be virulent for 104 days in Cheddar cheese. 

 They resist freezing, but, on the other hand, direct sunlight destroys 

 them in a few hours. 



Traum* has recently shown that tubercle bacilli in faeces and 

 lung discharges are no longer viable (as shown by the inoculation 

 test) after exposure for 3 months in a dry season but that they can 

 remain alive for at least 6 months in water. 



The vitality of the organism in the face of moist heat is of the 

 greatest importance owing to the frequent contamination of milk. 

 Bangf in his first experiments found 85 C the minimum temper- 

 ature to which milk should be heated with the object of destroying 

 the organism. Later he repeated his experiments and found that 

 70 C for one to two minutes is sufficient, though he was careful to 

 advise in practice the heating should be continued at 85 C. Delepine 

 on the other hand found that tubercle bacilli in cream are capable of 

 resisting a temperature of 85 C for 15 minutes and therefore 

 advised that the milk should be boiled. The heating of milk, even 

 to 85 C, has the effect of appreciably altering its flavour, and there 

 appears to be no way of avoiding this. In the case of animals, how- 

 ever, this fact is of no moment, and consequently it is advisable to 

 stipulate that the milk should be brought to boiling point and kept 

 there for 10 minutes. To satisfactorily sterilize milk for use as 

 human food, the best policy is to place the receptacle containing the 

 milk within an outer vessel containing water and to continue the 

 heating until the water has been at boiling point from 20 to 30 

 minutes. 



Inhalation is the most common method by which cattle become 

 infected, and the disease being strictly contagious the source of 

 infection is always a previous case. One of the principal ways 

 in which infection is distributed in a cow-shed is by means of the 

 tubercle bacilli contained in the expired air of animals infected with 

 pulmonary tuberculosis. In addition to this, tubercular disease of 

 the lung produces in many cases a considerable amount of expectora- 

 tion. A portion of this expectorate is discharged via the mouth 

 and nose but the bulk of it is swallowed, and the bacilli are thus 

 voided in the faeces. The bacilli are also occasionally excreted 

 with the urine and in those cases in which the uterus is the seat of 

 disease in the vaginal discharge. Infection of healthy animals is 



* Journ. Atner. Vet. Med. Assoc., Vol. LIL, No. 3, Dec, 1917, pp. 289-299, 

 through Vet. Rev., Vol. II., No. 2, May, 1918, p. 207. 



t Journ. Comp. Path., 1901, Vol. XIV., p. 233, Trans. 



