ON TUBERCULOSIS 193 



various textures of the bodies which, for the time being, 

 become its habitat, and where it develops and perpetuates, 

 and is communicated seriatim to other, or all, available or 

 suitable localities and organs within these bodies, until it 

 usurps and finally secures complete possession ; the physio- 

 logical yielding to the pathological regime^ amid a scene 

 of material and dynamic exhaustion altogether sui generis. 



We are inclined to think that, like its relative leprosy, 

 it at first finds a lodgment in and a foothold on inert and 

 devitalised materials or substances undergoing exfoliation 

 and removal from the system of the individual attacked, 

 such as are afforded in the situations usually chosen by the 

 bacillus in its first attempts at invasion ; as, for instance, in 

 the vesicular cavities of the pulmonary parenchyma and the 

 surface layers of the skin, where, in particular, its presence 

 is usually first observed after the influence of its patho- 

 logical presence has become manifest. 



In its origin, therefore, we see the operation of etio- 

 logical factors conducted along kindred lines to those which 

 can be traced in the evolution of zymotic disease generally, 

 and perceive to some extent the operation of the particular 

 etiological factors in the evolution of the individual 

 tubercular manifestations. 



If the infection be air-borne, we would naturally conclude 

 that the terminal air spaces of the lungs, where, from the 

 " calm and repose" of the residual air, the bacillary spores 

 could be dropped, deposited, or "sown" on the already 

 prepared soil of the exfoliating endothelium, would be 



ideal places " for the rearing of such organisms and the 

 propagation and distribution of their ripened seed. But, 

 on the other hand, if the infection be transferred in more 

 or less fluid or solid form from person to person, we 

 likewise see that the skin would most readily lend itself to 

 " culture of the organism, and could propagate and convey 

 it to the deeper-seated parts, alon^ which it would ulti- 

 mately reach and overrun seriatim by contiguity and 

 histological continuity the various vulnerable structures 

 and organs to which it might find access. 



The intestinal canal is another situation from which the 

 microbe secures admission into vulnerable regions by pass- 

 ing, along with articles of food and drink, through its 



