172 NUTRITION OF FARM ANIMALS 



of lipase has been shown to be reversible in some cases (211). 

 Whether this resynthesis be regarded as part of the process of 

 resorption or be classed as one of the metabolic processes is a 

 matter of indifference. In either case the material transmitted 

 to the blood current consists substantially of fats. 



The digested fats are contained in the lymph in the emulsified 

 form and in this state pass from the thoracic duct into the blood 

 of the subclavian vein. The blood itself, however, although 

 sometimes containing as much as i per cent of fat, does not 

 normally carry emulsified fats, and the fat globules entering it 

 from the thoracic duct do not long persist. The nature of the 

 change is still uncertain ; by some, it has been regarded as a 

 cleavage into fatty acids and glycerol and by others as a union 

 with proteins. But whatever the nature of the change it seems 

 to be well established that the fat of the blood exists in some 

 sort of combination which is soluble in water and diffusible 

 and which may be called for convenience " soluble fat." 



244. Storage of fat. A liberal supply of fat to the blood 

 from the digestive tract may give rise to a storage of reserve 

 fat in the adipose tissues (94) of the body. It is to be presumed 

 that this deposition of reserve fat is substantially a reversal of 

 the process, whatever it is, by which it was brought into solu- 

 tion in the blood, the " soluble fat " of the latter passing into 

 the cells and being there reconverted into the emulsified form 

 and so giving rise to the globules characteristic of fat cells. 



245. Formation of cell lipoids. The fats deposited in the 

 adipose tissues, as already implied, are a store of reserve ma- 

 terial, laid aside temporarily from the body metabolism when 

 the feed supply is more than adequate for immediate needs. 



The various more complex lipoids (37-39, 75), however 

 (cholesterins, . lecithins and other phosphatids, cerebrosids, 

 etc.), appear to be essential ingredients of protoplasm and to 

 perform specific functions in the cell. All these substances 

 have as their basis fatty acid molecules coupled with other 

 groups and it is a reasonable assumption that the former are 

 derived from the " soluble fat " of the blood and synthesized 

 in the cells into the specific lipoids as required. 



246. Manufacture of fats. But while the feed fats may 

 serve as a source of body fats, the organism is by no means 

 dependent upon the former for its supply of these substances, 



