428 YEAST 



able theory of many diseases which has been called the 

 " germ theory of disease," the idea, in fact, that we owe a 

 great many diseases to particles having a certain life of 

 their own, and which are capable of being transmitted 

 from one living being to another, exactly as the yeast plant 

 is capable of being transmitted from one tumbler of 

 saccharine substance to another. And that is a perfectly 

 tenable hypothesis, one which in the present state of 

 medicine ought to be absolutely exhausted and shown not 

 to be true, until we take to others which have less analogy 

 in their favour. And there are some diseases most assuredly 

 in which it turns out to be perfectly correct. There are 

 some forms of what are called malignant carbuncle which 

 have been shown to be actually effected by a sort of fer- 

 mentation, if I may use the phrase, by a sort of disturbance 

 and destruction of the fluids of the animal body, set up by 

 minute organisms which are the cause of this destruction 

 and of this disturbance ; and only recently the study of the 

 phenomena which accompany vaccination has thrown an 

 immense light In this direction, tending to show by experi- 

 ments of the same general character as that to which I 

 referred as performed by Helmholz, that there is a most 

 astonishing analogy between the contagion of that healing 

 disease and the contagion of destructive diseases. For it 

 has been made out quite clearly, by investigations carried 

 on in France and in this country, that the only part of the 

 vaccine matter which is contagious, which is capable of 

 carrying on its influence in the organism of the child who 

 is vaccinated, is the solid particles and not the fluid. By 

 experiments of the most ingenious kind, the solid parts 

 have been separated from the fluid parts, and it lias then 

 been discovered that you may vaccinate a child as much 

 as you like with the fluid parts, but no effect takes place, 

 though an excessively small portion of the solid particles, 

 the most minute that can be separated, is amply sufficient 

 to give rise to all the phenomena of the cow pock, by a 

 process which we can compare to nothing but the trans- 

 mission of fermentation from one vessel into another, by 

 the transport to the one of the torula particles which exist 

 in the other. And it has been shown to be true of some 

 of the most destructive diseases which infect animals, such 

 diseases as the sheep pox, such diseases as that most terrible 

 and destructive disorder of horses, glanders, that hi these, 

 also, the active power is the living solid particle, and that 



