244 PATHOGENIC BACTERIA IN MILK 



of the tubercle bacillus. The whole matter of virulence is one 

 very difficult to measure, or form precise opinion upon, owing to 

 the wide variations in specific virulence of the tubercle bacillus 

 and the impossibility of estimating the effect of dosage. From a 

 practical point of view it may be said that milk of a tuberculous cow 

 is most virulent when the udder is diseased and undiluted milk from 

 such udder is consumed in fairly large and continuous quantities. 



It is now generally admitted that the bovine tubercle bacillus 

 possesses greater pathogenic power than the human bacillus. Yet 

 this, of course, is a variable quantity, and is a factor relative to the 

 point at issue. Exaltation of virulence for one species of animal 

 does not necessarily prove an increased power for other species, 

 although such would be the general rule. There is evidence of 

 direct infection of man by accidental inoculation with the bovine 

 bacillus, and of indirect infection by means of infected milk. It is 

 with the latter only that we are concerned. Apart from the ques- 

 tion as to how much primary intestinal tuberculosis exists in the 

 human, and what percentage of it is due to cow's milk, there are 

 certain facts giving evidence of the virulence of milk which must 

 be mentioned.^ In the first place, after all deductions are made, 



^ We do not consider that the widespread discussion as to the inoculabihty 

 of the bovine bacillus upon man, or the degree of primary intestinal tuberculosis 

 in man, has up to the present yielded sufficiently definite results for inclusion in 

 the present volume. These are, and must remain for the present, matters rather 

 for clinical investigation and inquiry. Here we only have space to refer very 

 briefly to the question. 



As to the evidence of direct inoculation of the bovine bacillus, it must be 

 said that a number of cases are now on record appearing to prove that under 

 certain circumstances man may so contract tuberculosis (Tscherning, Pfeififer, 

 Hartzell, Mueller, De Jong, Lesser, Joseph, Trantmann, Ravenel, etc.). Such 

 cases seem to prove the possibility of inoculation, but it is well known that this 

 is not a common mode of contracting the disease, and Koch believes that in 

 many of these cases there were other sources of infection. 



The evidence as to the indirect conveyance of tuberculosis from the bovine 

 race to man by means of infected milk is of a nature which leaves little doubt 

 that such may occur. But in all probability it is neither as serious in degree or 

 wide in extent as has been supposed. Koch has laid down the view that 

 tuberculosis caused by aliments can only be assumed with certainty where the 

 intestine suffers first, that is, when a so-called primary tuberculosis of the 

 intestine is found. This condition, he states, is extremely rare, and therefore 

 there is no considerable infection by means of milk. But primary intestinal 

 tuberculosis cannot be considered as the only criterion of tubercular infection 

 by means of food, and even if that were so, there is evidence to show that 

 whilst primary infection of the abdomen is by no means so common as primary 

 infection of the respiratory tract, nevertheless it does occur. Many observers 



