248 DIGESTION. 



of acids, when we further bear in mind what slight means suffice 

 to convert oxide of ethyl into methyloxalic acid, or oxide of 

 amyl into valyloxalic acid, and when, finally, we consider the 

 various modifications which the protein-bodies experience under 

 the action of the ordinary atmospheric influences, causing them 

 even in some cases (as we see in putrefying cheese) to be partially 

 regenerated, we can scarcely conceive that any special expenditure 

 of force is necessary to move these masses in the manner indicated. 

 Although we must not suppose that isomerism and polymorphism, 

 or even the laws of ordinary chemical affinity, are able to afford a 

 true explanation of these metamorphoses and modifications of 

 known materials, it cannot be doubted that the same forces are 

 employed within the sphere of life as those which act in the 

 external world, and that a very slight increase of intensity is alone 

 necessary to produce the effects which we perceive in life. If, 

 however, the organism requires so slight a development of force to 

 effect these changes in matter, we shall hardly deem it necessary 

 to assume the existence of a special force of great intensity and 

 applicability to effect the ever-marvellous movements of organic 

 matter; but are rather led to the belief that the same simplicity 

 which nature exhibits in the use of material means, is unfolded on 

 a grander scale in the application of her forces. 



DIGESTION. 



As in the second volume of this work, we have treated of the 

 different juices which take part in the digestive process, and have 

 attempted to determine the functions which nature has assigned 

 to each of them, it might appear advisable, before reviewing this 

 process as a whole and in a general point of view, to examine more 

 closely the objects of digestion, that is to say, the nutrient matters 

 themselves in their relation to this process ; but as we have there 

 assumed that the reader possessed a general knowledge of the sub- 

 ject of nutriment, it will here be our best course to discuss the pro- 

 cess itself, before entering upon the digestibility of individual arti- 

 cles of food, and the action of the various digestive agents upon 

 them. 



From the earliest period at which it was attempted to apply 



