836 THE POPULAR SCIENCE MONTHLY. 



TISSUE-SELECTION IK THE GENESIS OF DISEASE. 



Br W. HENKY KESTEVEN, M. K. C. S. 



IT has occurred to the writer that the adoption of the germ theory 

 of disease necessarily involves the application of the theory of 

 evolution, and that here may be found a means of accounting for the 

 genesis of the various forms of disease. Germs are living matter ; 

 they must therefore be under the influence of those laws and forces 

 which condition all living matter. The most important of these, 

 or the one that most interests us in the present connection, is the 

 law of natural selection ; and it must be that germs, in common 

 with other forms of life, are under the influence of this law in 

 some shape. Natural selection is a general term which embraces 

 all other modes of selection, or provision for the "survival of the 

 fittest." Among these is sexual selection, and, taking a broad view, 

 we may also include selection by man. In order, then, to the at- 

 tainment of greater exactness, may we not give a name to that form 

 of natural selection which has been potent in bringing about the varia- 

 tions in the characteristics of those germs to which the differences in 

 the forms of disease are due ? Such a term may be found, I would 

 suggest, in " tissue-selection," as indicating the special means whereby 

 the constitution of the germs has been modified. The actual origin of 

 the bodies which have received the names of germs is not at present 

 determinable, and to say that they do not originate de novo, in decay- 

 ing matter or elsewhere, is only to reaffirm the axiom now pretty 

 generally admitted, Omne vivum e vivo. The fact that meets us here 

 is that these germs, call them bacilli, vibriones, bacteria, or what we 

 will, are met with almost universally in the atmosphere that we breathe. 

 It is with the " why and the wherefore " of their existence that we are 

 concerned. In looking for this, it will be necessary to consider the 

 facts of the life-history of these germs, and to try to discover how 

 they have been and are influenced by their surrounding conditions. 

 We find that the conditions favorable to the full vital activity of 

 these germs are a moderate temperature, moisture, and a resting-place 

 or nidus in some organic matter whose chemical constitution enables 

 it to afford the pabulum necessary for the maintenance of their exist- 

 ence. On the other hand, the influences antagonistic to their well- 

 being are excessive heat or cold, the action of certain chemical bodies, 

 and a condition of dryness. The last is certainly prejudicial, as it 

 seems to hinder their full vital activity. At the same time it can not 

 be considered absolutely obnoxious, as it is the means which favors 

 their locomotion in the atmosphere. Putting aside, for the mean while, 

 the thermometric and atmospheric conditions, we shall see that the 



