DISEASES OF THE OX AND SHEEP. 211 



hours destroyed the infective power of the virus, and nine 

 hours' exposure destroyed the virus in hoth the cases which 

 were tried. The bacterial fluid added to the solution of the 

 mercuric salt was in the proportion of 1 of the former to 100 

 of the latter. 



The above-mentioned observers arrive at the conclusion that 

 both the restraining and the killing powers of this salt are far 

 greater than those of any other known chemical substance. 

 Speaking generally, they hold that organisms which do not 

 produce disease are less strongly affected by the salt than 

 organisms such as the anthrax bacillus and the tubercle 

 bacillus, and other bacilli which produce disease. 



Causes. — Tuberculosis is, as our readers are probably aware, 

 characterised by the deposition of tubercular matter in different 

 parts of the body. The lungs, intestines, liver, spleen, 

 lymphatic glands, or other organs may be affected. As a result 

 of the disease, the tissues waste, and death may occur more or 

 less rapidly. Now the question naturally presents itself, ** By 

 what means are these changes brought about ? " This question 

 can now be answered far more clearly than was possible a few 

 years ago ; but even in these days of scientific exactitude the 

 word " cause " can only be used in a provisional sense. There 

 are yet many points admitting of considerable doubt in regard to 

 the causation of disease, and we do not say this so much from 

 the philosophical point of view, as from the stand-point of the 

 practical man. Owing to the recent improvements in that most 

 useful instrument of scientific research, the microscope, the 

 observer of this age has been introduced rather suddenly into 

 new worlds teeming with rich stores, and the mines of wealth 

 open to exploration are so immense that as yet we have not 

 had time to devote to this all-important question of '* germs " 

 anything like that attention which it deserves. 



Tuberculosis may be said to depend upon the presence of 

 tubercle-bacilli in different parts of the body of the animal which 

 is affected with it. The bacilli of tuberculosis were first found by 

 Koch, and the form and general character of these bacilli may be 

 seen from an inspection of the diagram on the next page. 



BaciUi, so much like these as to be scarcely distinguishable 

 from them, are present in the caseous tubercular deposits in cases 

 of tuberculosis in man, cattle, monkeys, and birds, and likewise 



14 * 



