ADDRESS. IxXXV 



If there were a kind of diseased structure, the histological elements of which 

 were capable of maintaining a separate and independent existence out of the 

 body, it seems to me that the shadowy boundary between morbid growth and 

 Xenogenesis would be effaced. And I am inclined to think that the pro- 

 gress of discovery has almost brought us to this point already. I have been 

 favoured by Mr. Simon with an early copy of the last published of the valu- 

 able " Reports on the Public Health," which, in his capacity of their Medical 

 Officer, he annually presents to the Lords of the Privy Council. Tlie Ap- 

 pendix to this Report contains an introductory essay " On the Intimate Pa- 

 thology of Contagion," by Dr. Rurdon 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 vaccination. A minute cut is made in 

 the skin, and an infinitesimal quantity of vaccine matter is inserted 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 wliat 

 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 confirmed 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 element in the vaccine lymph is non-difi'usible, and consists of 

 minute particles not exceeding -j-iyj-g-fr of an inch in diameter, which are 

 made visible in the lymph by the microscope. Similar experiments have 

 proved that two of the most destructive of epizootic diseases, sheep-pox and 

 glanders, are also dependent for their existence and their propagation upon 

 extremely small living solid particles, to which the title of microzymes is 

 applied. An animal suffering under either of these terrible diseases is a source 

 of infection and contagion to others, for precisely the same reason as a tub 

 of fermenting beer is capable of propagating its fermentation by " infection," 

 or " contagion," to fresh wort. In both cases it is the solid living particles 

 which are efficient ; the liquid in which they float, and at the expense of 

 which they live, being altogether passive. 



Now arises the question, are these microzymes the results of Homoc/enesis, 

 or of Xenogenesis ; are they capable, like the Torultv of yeast, of arising 

 only by the development of preexisting germs ; or may they be, like the 

 constituents of a nut-gaU, the results of a modification and individualization 

 of the tissues of the body in which they are found, resulting from the opera- 

 tion of certain conditions ? Are they parasites in the zoological sense, or are 

 they merely what Yirchow has called " heterologous growths " ? It is ob- 

 vious that this question has the most profound importance, whether we look 

 at it from a practical or from a theoretical point of view. A parasite may bo 

 stamped out by destroying its germs, but a pathological product can only 

 be annihilated by removing the conditions which give rise to it. 



It appears to me that this great problem will have to be solved for each 

 zymotic disease separately, for analogy cuts two ways. I have dwelt upon 

 the analogy of pathological modification, which is in favour of the xenogenetic 

 origin of microzymes ; but I must now speak of the equally strong analogies 

 in favour of the origin of such pestiferous particles by the ordinary process 

 of the generation of like from like. 



