CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 809 



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 tempo- 

 rarily depositing in itself some amount of fat ; and in what is 

 known as fatty degeneration there seems to be evidence 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 into the lacteals and so into the blood, from 

 which they rapidly disappear. We might infer from this that 

 an excess of fat thus entering the blood would naturally be dis- 

 posed of by being simply stored up in the available adipose tissue 

 without 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 

 intermediaries), 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 present 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 analysed, the amount of 

 fat in the body being among other things determined. The 

 other was fattened for a certain length of time on food whose 

 composition was known, and then killed and analysed. 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 fattening period. It is 

 clear that fat may be formed in the body out of something which 

 is not fat. 



507. There are two possible sources of this manufactured 



F. ii. 52 



