152 Lectures on Bacteria. [^ xiii. 



very imperfectly acquainted with its life-history, for we have 

 no certain information as to its place of sojourn during the in- 

 tervals of the fever, the form and mode of its conveyance from 

 one person to another, the formation of spores if any, or other 

 resting states. 



3. One of the most important results of the researches into 

 the Bacteria which are the exciting causes of disease is the dis- 

 covery of the contagium of tuberculosis, the Bacillus of tubercle 

 long since rendered familiar to us by Koch's publications (60). 

 Tuberculosis has received its name from the formation of new 

 substance or the degeneration by which it is characterised, and 

 which appear in the form of small knots or tubercles in the 

 tissue of the organs. The formation of tubercle is best known 

 in the lungs as pulmonary-tuberculosis, pulmonary consumption, 

 but it may occur in any organ and the lymphatic glands are 

 particularly subject to it. 



Tuberculosis attacks warm-blooded animals of every species 

 as well as man, and especially our ordinary domestic animals 

 and those used for experiments. The tuberculosis of horned 

 cattle is known by the name of pearly disease, bovine tuberculosis. 

 Different species show different degrees of susceptibility ; the 

 field-mouse is highly susceptible to infection, the domestic mouse 

 only slightly. The primary anatomical changes in the formation 

 of tubercle are in all cases the same. The succeeding ones and 

 the general character of the disease may be very dissimilar. 



In tubercle, at least in the fresh state, Koch and simulta- 

 neously with him Baumgarten demonstrated the presence of a 

 characteristic rod-shaped Bacillus. According to these observers 

 it is always there, though in very unequal quantities in different 

 cases. It passes into the ejected matter, the sputum of pulmo- 

 nary tuberculosis, and may be found in it. With due care it may 

 be kept pure and be cultivated pure through repeated generations 

 on stiffened blood-serum or in infusion of meat. 



Tubercular matter containing Bacilli, or still better the purely 

 cultivated Bacillus, introduced beneath the skin of susceptible 



