686 INFECTIOUS DISEASES. 



This aptitude or predisposition is of such importance that in 

 Moussu's opinion it should be regarded as one of the essential factors 

 in the development of tuberculosis. The cause of tuberculosis is 

 Koch's bacillus. It does not always produce its full effects in animals 

 born of healthy parents; but in one that suffers from a tuberculous 

 hereditary taint tuberculosis appears. 



Physiological and pathological researches cast considerable light 

 on this question. In tuberculous mothers the organism not only 

 suffers from the infection, but from a permanent intoxication which 

 interferes with normal metabolism in the vital organs and the ex- 

 changes between mother and foetus. If the microbes remain confined 

 to the system of the mother, their poisons are conveyed by the blood 

 and pass through the placental barrier. In a greater or less degree 

 they saturate the tissues of the little creature in process of develop- 

 ment, and communicate to it a peculiar hereditary taint. The effects of 

 this taint are often noticeable from the moment of birth, for com- 

 parative physiological and pathological investigations have shown that 

 the tissues of tuberculous animals assimilate given foods less perfectly 

 and are the seat of greater losses of all kinds than those of healthy 

 subjects. 



Although the disease itself, therefore, is not hereditary, it is other- 

 wise with the organic taint which plays so important a part in its de- 

 velopment. This organic taint consists in a special condition of the 

 tissues or cells of the parents, which show a diminished power of 

 resistance to the action of the germs of tuberculosis ; it is therefore 

 easy to understand how important a part these influences may play 

 under certain conditions. 



"Without doubt, in the case of bovine animals, the predisposition 

 could be neutralised in carefully managed studs by the immediate 

 isolation of the new-born under conditions which shield them from 

 tuberculous infection, and experiment has shown the benefits derived 

 from such precautions ; but it must not be forgotten that intelligently 

 managed studs are the exception, and that for a long time to come 

 we must in practice take cognisance of the actual conditions under 

 which the disease develops. 



The lesions of tuberculosis vary greatly in appearance, according 

 to the organs affected, though the method of development is always 

 identical. 



The primary lesion corresponds to what has been termed tuber- 

 culous granulation, or anatomical tubercle properly so called ; this, 

 the macroscopical, pathological entity, assumes the form of a small 

 prominent centre, semi-transparent, greyish, opaque or yellowish, ac- 

 cording to its age. 



