Its relation to Consumption in Man. 
309 
of Lyons, in 1873-74 confirmed the conclusions previously 
arrived at by Chauveau. It had thus been proved experi- 
mentally that tubercle could be conveyed from man to animals, 
and from animal to animal, in three ways, viz : by inoculation, 
ingestion, and inhalation. In addition to these modes of inducing 
the disease experimentally, it had been for some time, as the 
result of practical experience, the opinion of medical men and 
breeders of stock that this affection was hereditary. Soon after 
the experiments referred to had been conducted a new departure 
was made in the methods of carrying out pathological investi- 
gations, and the cultivation in the laboratory of disease-producing 
micro-organisms began. 
This led to our next great advance in the study of the 
disease, and Toussaint, in 1881, made the discovery that the virus 
could be cultivated apart from any animal body, but he was not 
aware at the time what the form or nature of that virus really 
was. In the following year Koch discovered in tubercular 
deposits the constant existence of a rod-shaped body which he 
considered the true cause of the disease, and named it the 
tubercle bacillus. Koch's discovery was inquired into and soon 
generally accepted. A method was thus established of deter- 
mining whether any morbid deposit in the lungs or other organs 
of man or animals was tubercular in its nature or not. It is 
true that more recent and extended bacteriological investigations 
show that this tubercle bacillus of Koch cannot be distinguished 
at the present time by any of the known tests from the bacillus 
of leprosy, or from the bacillus recently described by Lingard in 
the affection known as lupus in the face of the human subject. 
But as these diseases are totally different in their ordinary 
clinical characters from tubercle, there is not much danger of 
their being confounded with it ; and just as the microscope is the 
means of distinguishing between tubercle and other morbid 
deposits with similar appearances, so the naked-eye examina- 
tion proves the means of distinguishing diseases with similar 
micro-organisms, but general clinical characters different from 
tubercle. 
Prior to these experimental investigations and the discovery 
of the bacillus by Koch, tuberculosis was supposed to be, due 
to various causes, among which may be mentioned climatic 
influences, defective nutrition, exposure to hardships, over- 
work, excessive secretion — in fact, any and every influence 
calculated to produce debility. Since Koch's discovery these 
alleged causes have been considered as only predisposing or 
preparing the structures of the body for the reception of the 
disease-producing germs which are the true cause. What>- 
