MODEBN IDEAS OF SANITARY ECONOMY. 



59 



Also — "Fermentation, which we define an intestine motion 

 of mixed parts, that separates them in proportion to their 

 mobility, and resolves or combines them according to its 

 degree. So that this operation requires for its subject the 

 parts of a mixt which differ in mobility, that is, have 

 different degrees of tenuity; and in the next place it requires 

 a certain management of this motion, so that it be inherent 

 or intestine, and not loco pulsive" 



This theory of fermentation was with great success applied 

 to the solution of the food in the stomach, to diseases, and to 

 contagion and miasms. Liebig has brought it forward in the 

 same form, with the great power of illustration which modern 

 science has furnished. His conclusions are very well known, 

 and I need only give two sentences from his Letters^ p. 209: — 

 ** All the phenomena of fermentation, when taken together, 

 establish the correctness of the principle long since recognised 

 by Laplace and Berthollet, namely, that an atom or molecule 

 put in motion by any power whatever, may communicate its 

 own motion to another atom in contact with it." Then having 

 referred the same principles to putrefaction, and shown, that 

 in a similar way, disease may be produced and continuously 

 communicated, he says — " Hence according to the rules of 

 scientific research, the conclusion is entirely justified, that in 

 all cases where a putrefactive process precedes the occurrence 

 of an epidemic or contagious disease, or where the disease can 

 be propagated by means of solid, liquid, or gaseous products 

 of diseased action, and when no other cause for the disease 

 can be discovered, the substances which are in a state of 

 transformation are, in virtue of that state, to be regarded as 

 the proximate causes of the disease." Letter 18, p. 230. 



The whole reasoning, as given by him, is very clear and 

 full, and it is one of the most singular instances of a theory 

 made apparently very early and in the darkest periods of 

 science, receiving illustrations now at the hand of science, 

 with scarcely any difference of views, but only a clearer per- 

 ception of the meaning of the words used. 



