Chap. IX.] NUTRITION AND METABOLISM. 191 



the period of activity this inogen undergoes katabolism with 

 the formation of carbonic acid and sarcolactic acid, and this pro- 

 cess is accompanied by the shortening of the muscle fibre. In 

 any case it seems clear that the katabolism of the muscle fibre 

 at the moment of contraction, by which carbonic acid and sarco- 

 lactic acid are produced, is not the result of the direct oxidation 

 of the substance of the fibre at the expense of the oxygen of 

 the blood. A muscle containing no free oxygen will contract 

 in an atmosphere perfectly free of oxygen. The change is a true 

 katabolism or breaking down of more complex into less com- 

 plex molecules. The katabolism of the inogen may be likened 

 to an explosion, where the explosive material, more or less 

 suddenly, by a rearrangement of molecular groupings, falls from 

 a state of unstable to one of stable equilibrium. 



Of the metabolism of nervous tissue we know still less than 

 of that which occurs in muscular tissue. But it is probable 

 that here too, by the vital activity of the protoplasmic element 

 in each cell, there is produced a mesostate which, at the moment 

 of activity, passes by katabolism into waste products, so called, 

 of less complex composition. 



A metabolism similar in principle goes on in fat cells. Here 

 the inherent vital activity of the protoplasm of certain connec- 

 tive tissue cells, causes the production of this peculiar storage 

 tissue. It is exceedingly improbable that there is anything like 

 a direct deposition in the fat cells of fat absorbed into the 

 lacteals. Each individual has, by its vital activity, to build up 

 its own tissues for itself. 



So far, however, we have assumed in each cell a protoplasmic 

 element which initiates the temporary or more enduring storage 

 of a mesostate. How is this protoplasm itself elaborated ? At 

 present we do not know. We may well suppose that it results 

 from a process of metabolism, and is probably preceded by one 

 or more anabolic mesostates. We know that the protoplasmic 

 pale corpuscles or leucocytes are largely produced in the lym- 

 phatic glands. But how ? 



In any case we may fairly regard the complex chemical 

 changes which go on within the body as a series of ascending 



