APPENDIX E. cxxvii 



properties, still the ascertained existence of even one ex- 

 ceptional case amongst maladies so contagious as sheep- 

 pox, seems to me absolutely irreconcileable with the truth of 

 the ' germ-theory,' more especially when this theory was 

 started principally to explain the phenomena of such highly 

 contagious diseases l . 



In rejecting the ' germ-theory/ then, must we confess our 

 absolute ignorance on the subject (a course always better 

 than the adoption of an untenable theory), or are there facts 

 to guide us to another view as to the nature and origin of 

 the poisons of these infectious diseases ? 



It surely is a vice in argument to suppose that the increase 

 of the virus within the body in these affections is only to be 

 accounted for by a process of organic reproduction. The 

 power of self-multiplication by division is peculiar to living 

 things, but an actual increase of any substance may occur by a 

 process of growth alone, without the aid of self-multiplication. 

 Growth, however, takes place in not-living as well as in 

 living matter ; and, fundamentally considered, it only means 

 increase in the quantity of the substance which grows, 

 whether we have to do with the substance of a muscle, with 

 a crystal, or with a complex organic poison. Liebig says : 

 ' A substance in the act of decomposition, added to a mixed 

 fluid in which its constituents are contained, can reproduce 

 itself in that fluid/ And in illustration Sir Thomas Watson 

 writes : ' Thus the virus of small-pox (which virus is formed 

 out of the blood) causes such a change within the blood as 

 gives rise to the reproduction of the poison from certain 

 constituents of that fluid : and whilst the process is going on 



. l Inoculation with the blood of a person suffering from measles has 

 in several cases failed to reproduce the disease. The different severity of 

 small-pox taken in the ordinary way, and that induced by ' inoculation ' 

 of the matter of a small-pox pustule, is also quite inexplicable in accord- 

 ance with the ' germ-theory,' although both facts are quite reconcileable 

 with the view about to be mentioned. 



