Chemical Physiology and Pathology, 533 



carbonic acid, ammonia and water, the elements of the 



nourishment of plants. The inorganic constituents of 



the animal body are, according to the views of most authors, 

 introduced into the system in the articles of food, and all 

 authorities agree on this point, that the animal body cannot 

 form these constituents from the elements, or change them 

 into others, when introduced. 



II. Pathological chemistry, in as much as life manifests 

 itself solely by an unceasing change of substance, regards 

 disease (i. e. a group of vital phenomena, which deviate in 

 any degree from the normal) as a peculiar condition of the 

 exchange of substance, and endeavours under this idea to 

 fathom its causes ; while nosology represents disease as a 

 compound of symptoms, and assumes for each one a vis a 

 tergo, which cannot be any further explained, such as an acid 

 matter, a parasite, &c. 



Poison, Contagion, Miasma. Liebig expresses himself thus 

 on these subjects. Nutritious substances are those which 

 lose their properties under the influence of the vital powers, 

 without exerting a chemical action on the organ that operates 

 upon them. Other substances alter the direction, the force, 

 or the intensity of the resistance of the vital powers, in 

 consequence of which the function of their organs is altered. 

 They cause a disturbance by their mere presence, or because 

 they are themselves undergoing transmutations, — these are 

 medicines. If their tendency to unite themselves with the 

 constituents of the organs be stronger than the resistance 



of the vital powers, they work as poisons. A very 



peculiar class of substances, which may be produced by de- 

 composition of a particular sort, work as deadly poisons, not 

 from their power of forming new combinations, or because 

 they contain a positive poison, but from the condition in 

 which they are, and which they impart to the organism, 

 {contagions) : Liebig compares the operations of these bodies 

 to fermentation, and in this rests on the position laid down 



