SYNTHESIS OF THE ALBUMINS. 29 



Should this theory as to the origin of the albumins in plants prove 

 correct, it would thus be clear that all three of the great classes of 

 food-stuffs which animals require for their existence are formed 

 synthetically under the influence of sunlight, and through the 

 special activity of chlorophyl. Subsequent changes, of course, 

 take place, whereby the albumins, like the carbohydrates and fats, 

 are transformed into those peculiar modifications of the original 

 compounds which are required by the various organs of the plant. 

 These changes, however, are in a manner of only secondary impor- 

 tance, and not to be compared in complexity to the elaborate syn- 

 thetic processes which have previously occurred. They are brought 

 about through the specific activity of the various cells of the 

 organism, and in part, at least, through the agency of ferments. 



The food-stuffs which are thus elaborated by the plants cannot all 

 be utilized by the animal as such, however, and previous to their 

 assimilation they are further modified. The albumins are thus trans- 

 formed into albumoses and peptones, starch is inverted to maltose, 

 and the fats are decomposed and saponified. These processes of 

 what may be termed primary assimilation, or digestion, render the 

 food-stuffs capable of passing through the mucous membrane of the 

 gastro-intestinal canal. During this passage the albumoses and 

 peptones are retransformed into albumins proper, maltose is changed 

 into glucose, and the fats are reconstructed from their two com- 

 ponents. Subsequently all these bodies are further modified accord- 

 ing to the character of the tissues in which they are to be utilized. 

 Ultimately, however, they give rise to the formation of those simple 

 substances which plants require for their existence that is, into 

 carbon dioxide, water, and certain nitrogenous bodies which readily 

 give rise to the formation of ammoniacal salts. 



The passage through the body of the various elements which go 

 to form the tissues and organs of both plants and animals, and the 

 various chemical and physical changes which are here involved, con- 

 stitute the phenomena of metabolism ; and we may thus state that 

 physiological chemistry deals primarily with the various metabolic 

 processes which occur in the living world. 



Before proceeding to a study of these various changes in the 

 animal body, however, it will be well to review the chemical proper- 

 ties and the composition of the various food-stuffs which enter into 

 the construction of its tissues. We shall accordingly consider the 

 chemistry of the albumins, the carbohydrates, and fats, and then 

 attempt to follow the course of these bodies through the living 

 organism so far as this is possible with the present state of our 

 knowledge. 



