METABOLISM 



219 



FIG. 116 



the chemical changes in the body-protoplasm rather than to food in the 

 intestinal wall. 



The anabolic processes of the organism are as yet too little known in 

 their details to warrant even an attempt to describe them here. The 

 reason for this lies in the fact that the chemistry of the anabolic processes 

 is of unique complexity, besides being everywhere deeply hidden in the 

 protoplasm of the intestinal walls or of the tissue-cells. 



The katabolic processes of the body, in which the tissue-protoplasm 

 is chemically simplified in its life-activities, are somewhat more acces- 

 sible than the anabolic processes, and in consequence they have been 

 better learned. In plants the opposite is true. The vital processes of the 

 vegetable kingdom are essentially anabolic, while the phenomena of 

 animal life depend on chemical reactions of a katabolic kind. It is by 

 katabolism that an animal's body 

 liberates the energy by which it lives. 

 To be exact, life considered biologi- 

 cally is metabolism, especially in its 

 katabolic phase. 



Organic Growth and Repair in its 

 histological aspects is not a subject 

 germane to our present purpose, but 

 it is necessary for completeness' sake 

 to look briefly at the processes of 

 anabolism in this respect. Until the 

 adult stature is attained the body 

 grows. Gaps made by wounds are 

 filled in by new tissues, and lost blood, 

 etc., are gradually regenerated. It is, 

 of course, a prime characteristic of 

 living matter to be, from use or de- 

 generation, continually wasting, and 

 this loss must be as continually re- 

 placed. These and the other wastes of animal tissue the food and the 

 respiratory oxygen restore. As we have seen already in Chapter IV, only 

 the proteids of food are capable of supplying adequately both tissue and 

 energy to the animal organism, the other " proximate principles" having 

 only special values in this direction. How then are the proteid anabolic 

 processes conducted to this primary organic end of growth and repair ? 



Pfluger's hypothesis has much interest: "In the making of cell-sub- 

 stance, i. e., of living proteid, out of the proteid of the food a change 

 occurs in the latter, the nitrogen-atoms going into a relation with the 

 carbon-atoms like that in cyanogen, with probably the absorption of 

 much heat." This introduction of the cyanogen-radical into the vital 

 molecule of the tissues introduces into it lively energy as motion, heat, 

 etc., but also something which is of more immediate interest here the 

 power of spontaneously growing and of wasting. In a word, proteid 

 anabolism means the power of spontaneous metabolism, of interchanging 



Fat cells from the subcutaneous connec- 

 tive tissue of an embryo calf of 45 cm. 

 in length. In a the fat globules are few 

 and small; in 6 some have coalesced; in c 

 still more; while in d nearly the whole 

 mass of the cell is fat. (Ranvier.) 



