APPEXDIX E. cxlv 



surfaces of ordinary individuals ? And does not the diminish- 

 ing contagiousness of different diseases seem to be due to 

 the fact that off-cast particles in these affections are less and 

 less capable of acting upon the healthy fluids and mucous 

 surfaces of the body, but require them to be altered, now by 

 one set of agencies affecting the general health and now 

 by another, before any of such particles can initiate those 

 changes which lead to the evolution of similar specific 

 poisons within the body ? Hooping-cough, measles, scarlet 

 fever, and smallpox, would, in this case, be merely the last 

 terms of a series, differing from the other members simply 

 in degree, but not in kind — and therefore as capable of being 

 generated de novo as either of the others, although much 

 more capable than they are of being disseminated by means 

 of contagion. 



If we reject this notion, what remains for us ? The germ- 

 theory is quite untenable — the analogy which has been 

 thought to exist between the causes and nature of certain 

 diseases and the specific and unalterable characters of living 

 organisms is erroneous in both its aspects. And even if the 

 diseases are now only propagable by contagion — =just as the 

 higher hving things are propagable by reproduction — they 

 must nevertheless have originated once ; and, if once, why 

 not now.? Or, declining to admit even so much, shall we 

 refuse to bear our own burdens .? Shall we shift the difficulty, 

 and suppose that the poisons of syphilis, measles, scarlet 

 fever, small-pox, and other diseases, have been evolved 

 amidst the unknown conditions obtaining upon the surface 

 of an unknown world, whose disruption has scattered .them 

 broadcast, and conveyed them to us, with other never-dying 

 germs, upon the verdant surface of a ' moss-grown frag- 

 ment ' "i With such alternatives, surely our choice cannot be 

 doubtful. 



If we turn to a sober survey of the facts which lie befdre 



VOL. II. k 



