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REPORT. | xxi 
petits Modes in which the Virus or Microbe enters the Body. 
21. The bacillus tuberculosis has been proved to enter the body, and to kill the animal 
by causing the growth of tubercles, in the following ways :— 
(1.) Inhalation—into the air passages and lungs. 
(2.) Swallowing—into the alimentary or digestive system. 
(3.) Direct introduction—into the sub-cutaneous or sub-mucous tissue by means of a 
scratch or cut or sore in the skin or mucous membrane. 
It is also supposed to be directly transmitted by— 
(4.) Heredity. 
22.—(1.) Inhalation.—Owing to the fact that the signs of disease are most com- 
monly found in the lungs, inhalation would appear to be the commonest way in which 
the disease is dontvatbad This has been tested by comparative experiments, in which 
animals inhaled tubercular secretions so minutely divided as to admit of the bacilli 
being distributed in a current of air, thus closely imitating that distribution of the 
virus which occurs when a tuberculous animal coughs, &c. The results of these 
experiments have been almost invariably positive, the animals breathing such infected 
air rapidly succumbing to the disease. 
23. Co-habitation, therefore, of the diseased and healthy animals is a fertile source 
of spread of the malady. 
24.—(2.) Swallowing.—Numerous experiments have similarly been performed upon 
the possibility of the tubercular virus entering the body through the alimentary canal. 
In these experiments, tubercular secretions, 7.¢., mucus, saliva, milk, &c., portions of 
tubercles from diseased tissues and cultures of the bacilli have been swallowed by 
various animals (calves, pigs, sheep, rodents, fowls, &c.), with the effect that the 
disease has fatally followed the ingestion of such infective material. 
25. It is obvious, therefore, that the digestive fluids do not necessarily exert an 
injurious influence upon the poisonous bacilli. 
26.—(3.) Direct introduction into the tissues beneath the skin or beneath the mucous mem- 
branes.—If tubercular material, that is to say, secretions from a tubercular animal, or 
portions of tubercles be introduced into the loose tissues beneath the skin or mucous 
membranes the bacilli cause a local inflammatory swelling (i.e, a tubercle) at the 
seat of infective inoculation, and then grow along the lymphatic vessels, causing 
similar inflammation of these latter, and, finally, reach the nearest glands. These also 
become diseased, and from them the microbes pass through the large lymphatic 
vessels, which subsequently discharge into the veins, so that the virus is distributed 
throughout the body, and the disease, at first local, becomes general, affecting most of 
the organs (but especially the lungs, see pars. 37 and 42). 
27. Undoubted instances have been laid before us of such inoculation occurring ; 
and others are on record in which the human being has become affected with 
the disease by the microbe entering the system through a scratch or sore on the 
hands which have been brought in contact with tubercular sores or secretions. 
28. Similarly, cases probably falling within this category have been recorded, and 
one or two stated in the evidence, in which a bull has given the disease to cows, and the 
converse has also occurred, namely, that a bull has contracted the disease from cows. 
In the former of these instances, of course the virus may have been contained in 
the secretions, and it may have thus reached the ovary and so affected the system 
enerally. 
. 29.—(4..) Heredity.— While it is undeniable that the disease runs through certain 
families or strains, there is considerable doubt as to whether this is simply because 
the tissues of one particular breed or race are especially favourably disposed to nourish 
the tubercle bacillus, or whether the bacillus is actually contained in the ovum or 
spermatozoon, and so becomes a constituent part of the embryo and fostus, and 
develops within the uterus. The former view has already been referred to. 
30. In favour of the latter, it may be said that Baumgarten has actually, in the 
rabbit, observed the bacillus within the ovum, and, further, that the bacilli have, by 
different observers, frequently been seen mingled with active spermatozoa. 
31. Finally, in one striking case found by Professor Johne, of Dresden, an unborn 
calf of seven months intra-uterine growth, was discovered to present numerous 
tubercles in its lungs, showing that if the ovum had not been inoculated, it had 
received the virus through the placenta, which amounts practically to the same thing. 
eee intra-uterine infection has been shown to be more than probable in the human 
ing. 
Q. 7528 
Inhalation. 
Swallowing. 
Q. 7529. 
Q. 4909. 
Direct intro- 
duction. 
Q. 4891, 
4892. 
Heredity. 
Q. 2884. 
