THEIR MODE OF ACTION. 375 



particles of the sugar contained in it, both would sim ri- 

 taneously disappear when the fermentation was completed. 

 But yeast requires a much longer time for decomposition 

 than sugar, so that after the latter has completely disappeared, 

 there remains a much larger quantity of yeast than existed 

 in the fluid at the commencement of the fermentation, — yeast 

 which is still in a state of incessant progressive transformation, 

 and therefore possessed of all its peculiar properties. 



The state of change or decomposition which afFects one particle 

 of blood, is imparted to a second, a third, and at last to all the 

 particles of blood in the whole body. It is communicated in 

 like manner to the blood of another individual, to that of a third 

 person, and so on — or, in other words, the disease is excited in 

 them also. 



It is quite certain that a number of peculiar substances 

 exist in the blood of different men, in that of the same 

 man at different periods of his development, and in that of 

 animals. 



The blood of the same individual contains, in childhood and 

 youth, variable quantities of substances, which are absent from 

 it in no other stages of growth. The susceptibility of contagion 

 by peculiar exciting bodies in childhood, indicates a propagation 

 and regeneration of the exciting bodies, in consequence of the 

 transformation of certain substances present in the blood, and 

 in the absence of which no contagion would ensue. The form 

 of a disease is termed benignant, when the transformations 

 of two constituents of the body not essential to life, are simul- 

 taneously completed without the other parts taking a share in 

 the decomposition ; it is termed malignant when they affect 

 essential organs. 



It cannot be supposed that the different changes in the 

 substance of the existing organs, by which their constituents are 

 converted into fat, muscular fibre, substance of the brain and 

 nerves, bones, hair, &c, and the transformation of food into 

 blood, can take place without the simultaneous formation of new 

 compounds which require to be removed from the body by the 

 organs of excretion. 



In an adult these excretions do not vary much either in their 



