14 



to a good deal of discussion. These rod-shaped bacilli have been 

 shown to exist, in all cases of human tuberculosis, in the sputum, 

 in caseating scrofulous glands, and in the tubercular masses in 

 the lungs. Pure cultivations of these bacilli when introduced 

 beneath the skin of susceptible animals such as rabbits, guinea- 

 pigs, cats, and field-mice, always produce after three, four, or more 

 weeks, the typical tubercular lesions ; swollen lymphatic glands, 

 deposits in the spleen, liver, and lungs, and enlargement and 

 caseation of the bronchial glands. Different species of animals 

 present very different degrees of susceptibility ; the domestic mouse 

 is not easily affected, whereas the field-mouse is highly susceptible ; 

 and as eveiy practical physician knows, in certain families of the 

 human species there is an unmistakable liability, an inborn 

 tendency to suffer from tuberculosis, whereas other families en- 

 tirely escape. Wherein lies this great difference of susceptibility"? 

 In what way do the micro-organisms either in tuberculosis or 

 anthrax or relapsing-fever influence the economy? how do they 



produce the disease? Why should some animals resist their power 

 and others be overwhelmed by them ? Recent investigations seem 

 to me to throw some light on these points, and in some degree to 

 answer these questions. 



When certain forms of bacilli, of the so-called non-pathogenic 

 character, are introduced into the blood of the lower animals, even 

 in large numbers, their existence is of comparatively short dura- 

 tion, and they speedily disappear. The living blood has the 

 power of destroying them. In three hours according to Wysso- 

 kowitsch none are present even though enormous numbers are 

 injected. They are deposited in the liver, spleen, and medulla of 

 bone, and soon die if they do not contain spores. If spores are 

 injected these live much longer, those of bacillus subtilis being still 



