APPENDIX E. cxxi 



has gradually grown up an unwillingness in the minds of 

 many to believe that these contagious diseases can arise de 

 novo. And, this being one of those beliefs which tends to 

 curb inquiry, and to check the possible growth of sanitary 

 knowledge in certain highly important directions, it seems to 

 me necessary to look with scrutinising care to its founda- 

 tions — not only with the view to the advancement of 

 medical science, but with the direct object of removing 

 all checks which may exist to the growth of sanitary 

 precautions against the origin of these most pestilential 

 affections. 



Let us see, then, how far the ' germ-theory' fulfils the con- 

 ditions which all good theories do fulfil — how far it explains 

 a great number of the phenomena in question, without being 

 irreconcileable with others. 



The advocates of the ' germ-theory ' have always rested 

 their belief in it, in the main, because they considered that it 

 offered a ready explanation of the increase of the virus of 

 the contagious diseases within the body of the affected 

 person. This increase, they suppose, is not otherwise to be 

 explained. All other considerations brought forward in 

 support of the theory are just as explicable by another 

 supposition. Fully admitting that the occurrence of a pro- 

 cess of organic self-reproduction would be a very adequate 

 way of accounting for the increase of the infecting material, 

 we must see whether this mere hypothesis can be reconciled 

 with other characteristics of these affections. In the first 

 place, it may be asked, whether such a process is actually 

 known to constitute the essence of any general diseases. 

 Because, if so, those in which it does occur, ought, in the 

 event of the hypothesis being true, to present a close 

 similarity to the diseases in which such a process is supposed 

 to occur. 



Now there are certain general diseases which do un- 



