THE PRESENT EVOLUTION OF MAN — PHYSICAL 287 



cannot be doubted, and this in spite of the greater 

 attention which is now-a-days paid in some places to 

 ventilation ; for the best ventilation that exists in such 

 houses as we inhabit, though it may help to maintain 

 the vitality by ensuring an abundant supply of un- 

 vitiated air, is not of a kind to sweep the pathogenic 

 organisms from the dwellings. 



The conditions under which we live are such that, 

 normally, every individual amongst us is exposed to in- 

 fection, that is, we all at one time or another enter 

 rooms inhabited by tuberculous patients ; but such has 

 been the evolution of resisting power in our race, that 

 only one-seventh of us perish from consumption, while 

 six-sevenths of us live immune to the disease, or recover 

 from it, and die from other causes. A notable fact in 

 this connection is the often evenly-balanced nature of 

 the struggle between the microbes and the phagocytes. 

 Many of us are resistant under almost any circumstances ; 

 many others easily contract the disease, and fall a rapid 

 prey, even under circumstances the most unfavourable 

 to it to be found in our land ; but very many others 

 exist in the border space between immunity and sus- 

 ceptibility. Such people, when their vitality is lowered, 

 or under other circumstances favourable to the bacilli, con- 

 tract the disease, but when their vitality is raised, or when 

 the environment becomes less favourable to the patho- 

 genic micro-organisms, defy it, or, if they are already 

 diseased, recover. Even when they do not recover the 

 disease usually runs a prolonged course in them ; there 

 is a lengthened struggle between the microbes and the 

 phagocytes, and we then behold the phenomena of chronic 

 phthisis. Laennec said that a patient does not die of 

 his first attack of tuberculosis ; that is, a patient of the 

 highly resistant type, which is the normal in our race. 

 Less resistant individuals, who have lapsed back to the 

 ancestral condition of greater susceptibility, undoubtedly 



