THE CAUSATION OF DISEASE. 223 



the best disciplined, the best equipped, the most skilfully 

 commanded troops. Since the introduction of firearms, bodily 

 strength and activity play far less part in the result than 

 formerly. Modern warfare, moreover, does not lead to the sur- 

 vival of the fittest, but rather to a destruction of them, since 

 the best physical types are chosen for soldiers, bodily weakness 

 exempting from service. 



Infanticide is also largely practised by primitive man. This 

 and warfare have doubtless been the chief checks to his increase. 

 But no doubt disease plays some part also. 



And here let it be observed that disease is a necessary evil. 

 Let no man lay to himself the flattering unction that any por- 

 tion of the animal kingdom can ever be wholly free from disease. 

 This would be impossible under any theoretical system of living 

 which he might devise. We have good reason to believe that 

 pathological variations must ever and anon occur under the most 

 favourable conditions which can be commanded — i.e., an indi- 

 vidual may vary in an unfortunate direction, independently of 

 any distinctly pathogenic E on the part of his parents. He 

 may, for instance, vary in such wise that under an averagely 

 hygienic E he will develop tubercle, rheumatism, or other 

 disease ; and such unhappy variation, does not, as I have already 

 insisted, necessarily imply a lack of bodily vigour, since, in the 

 case of many of the tt germ " diseases, an individual may in 

 all respects be healthy save in his ability to resist the attack 

 of some specific germ. 



But apart from such subtle tissue-variations, which render 

 the organism apt to take on pathological change under E's 

 which, to the community at large, are normal, patho- 

 logical variations which are quite obvious and palpable not 

 infrequently occur. I allude to such cases as hydroce- 

 phalus, idiocy, and monstrosity. Children thus afflicted may 

 be born to perfectly healthy parents. No doubt, in some 

 at least of these cases, there is a bad family history ; and 

 in others the mother may have been exposed, during gesta- 

 tion, to some form of mal-E, which, with due care, might 

 have been avoided. Nevertheless, it may with certainty be 

 asserted that such abnormal beings must inevitably occur 

 from time to time, even although the parents be selected after 



