CHAP, iv.] METABOLIC PROCESSES OF TIIK IJODY. 77:! 



oration thero 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, chiefly through the intermediate passage of the 

 lacteals, into the blood, from which they rapidly disappear 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 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 con- 

 nective-tissue corpuscles swallow the fat brought to them after the 

 fashion of an amosba, 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 de- 

 termined. 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 fat. 

 The carbohydrates of the food form one source. In treating of 

 digestion ( 282), we referred to the possibility of carbohydrates 

 during digestion in the alimentary canal becoming by fermentation 

 converted into butyric acid ; and we suggested that higher and 



