CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 607 



once urged, the simpler proteid constituent of living substance 

 obviously contains what we may call a fatty radicle, so that we 

 might expect fat to be formed out of its metabolism. And as 

 a matter of fact not only in adipose tissue, but in every part of 

 the body, living substance is continuously giving rise to and 

 temporarily depositing in itself some amount of fat, and in 

 what is known as fatty degeneration there seems to be evi- 

 dence of the formation of fat out of proteid material. 



On the other hand, we have traced the fats taken as food, 

 and found that they pass with comparatively little change from 

 the alimentary canal, chiefly through the intermediate passage 

 of the lacteals, into the blood, from which they rapidly dis- 

 appear after a meal. We might infer from this that an excess 

 of fat thus entering the blood would naturally be disposed of 

 by being simply stored up in the available adipose tissue with- 

 out any further change ; we can imagine that the fat, not 

 immediately wanted by the economy, passes in some way from 

 the blood to the connective tissue (the white blood corpuscles 

 which appear loaded with fat after a meal possibly acting as inter- 

 mediaries), and that the connective tissue corpuscles swallow the 

 fat brought to them after the fashion of an amoeba, not digesting 

 it but simply keeping it in store until it was wanted elsewhere. 



What do experiments teach on this matter ? 



In the first place, it is evident that in an animal fattened 

 on ordinary fattening food, only a small fraction of the fat 

 stored up in the body can possibly come direct from the fat 

 of the food. Long ago, in opposition to the views of Dumas 

 and his school, who taught that all construction of organic 

 material, that all actual manufacture of living substance or 

 even of its organic constituents, was confined to vegetables 

 and unknown in animals, Liebig shewed that the butter pres- 

 ent in the milk of a cow was much greater than could be 

 accounted for by the scanty fat present in the grass or other 

 fodder she consumed. He also urged, as an argument in the 

 same direction, that the wax produced by bees, which though 

 having a different composition from fat may be used as an 

 analogy, is out of all proportion to the wax or allied bodies 

 contained in their food, consisting as this does chiefly of sugar. 

 And it has since been shewn in many ways that, in fattening 

 animals, the fat accumulated in the body cannot be accounted 

 for by the fat which has been taken in the food. It has been 

 proved by direct analysis. Thus of two young \pigs, as much 

 alike as possible, of the same litter, one was killed and analyzed, 

 the amount of fat in the body being among other things deter- 

 mined. The other was fattened for a certain length of time 

 on food whose composition was known, and then killed and 

 analyzed. It was found that for every 100 parts of fat in the 

 food 472 parts of fat were stored up in the body during the 



