260 BIOGENESIS AND ABIOGENESIS viii 



Public Health," wliich, in his capacity of their 

 medical officer, he annually presents to the Lords 

 of the Privy Council. The appendix to this 

 report contains an introductory essay " On the 

 Intimate Pathology of Contagion," by Dr. Burdon- 

 Sanderson, which is one of the clearest, most 

 comprehensive, and well-reasoned discussions of a 

 great question which has come under my notice 

 for a long time. I refer you to it for details and 

 for the authorities for the statements I am about 

 to make. 



You are familiar with what happens in vaccina- 

 tion A minute cut is made in the skin, and an 

 infinitesimal quantity of vaccine matter is mserted 

 into the wound. Within a certain time a vesicle 

 appears in the place of the wound, and the fluid 

 which distends this vesicle is vaccine matter, in 

 quantity a hundred or a thousandfold that which 

 was originally inserted. Now what has taken 

 place in the course of this operation ? Has the 

 vaccine matter, by its irritative property, produced 

 a mere blister, the fluid of which has the same 

 irritative property? Or does the vaccine matter 

 contain living particles, which have grown and 

 multiplied where they have been planted ? The 

 observations of M. Chauveau, extended and con- 

 firmed by Dr. Sanderson himself, appear to leave 

 no doubt upon this head. Experiments, similar 

 in principle to those of Helmholtz on fermentation 

 and putrefaction, have proved that the active 



