40 THE FLOATING-MATTER OF THE AIR. 



physical conditions, to evolve from it living things ; the 

 other (without wishing to set ])ounds to the power of 

 matter) affirming that, in our day, life has never been 

 found to arise independently of pre-existing life. I 

 belong to the party which claims life as a derivative of 

 life. The question has two factors — the evidence, and 

 the mind that judges of the evidence ; and it may be 

 purely a mental set or bias on my part that causes me, 

 throughout this long discussion, to see, on the one side, 

 dubious facts and defective logic, and on the other side 

 firm reasoning and a knowledge of what rigid experi- 

 mental inquiry demands. But, judged of practically, 

 what, again, has the question of Spontaneous G-enera- 

 tion to do with us ? Let us see. There are numerous 

 diseases of men and animals that are demonstrably the 

 products of parasitic life, and such diseases may take 

 the most terrible epidemic forms, as in the case of the 

 silkworms of France, referred to at an earlier part of thi& 

 essay. Now it is in the highest degree im porta nt ta^ 

 know whether the parasites in question are sp ontaneousl y 

 developed, or whether they have been wafted^/rom with- 

 out to those afflicted with the disease. The means of 

 prevention, if not of cure, would be widely different 

 in the two cases. 



But this is not all. Besides these universally ad- 

 mitted cases, there is the broad theory, now broached 

 and daily growing in strength and clearness — daily, in- 

 deed, gaining more and more of assent from the most 

 successful workers and profound thinkers of the medical 

 profession itself — the theory, namely, .that-coatagious 

 disease, generally, is of this parasitic character. Had I 

 any cause to regret having introduced this theory to 

 your notice more than a year ago, that regret should 

 now be expressed. I would certainly renounce in your 

 presence whatever leaning towards the germ theory 



