CHAPTER III. 



THE SYNTHESIS OF FATS. 



A consideration of the salient features of the physiological 

 significance of fats has been given in the first volume,* in 

 which place the consideration was retained for the sake of a 

 closer association of the characterization and other properties 

 of fats with the physiological problems involved. For this 

 reason a general survey only, with such departures into detail 

 as necessity demands, will be given on the present occasion. 



In the plant fats are commonly associated with the reserve 

 food in seeds, spores, and vegetative perennating organs, 

 but in smaller quantity they are probably present in all living 

 cells. As a food they have considerable value in that on physio- 

 logical combustion they yield more energy weight for weight 

 than either protein or carbohydrate, the relative energy- 

 producing values being roughly 5:3:2 respectively.f 



The immediate question is the origin of fats : Have they a 

 photosynthetic origin from raw material in much the same 

 way as carbohydrates, or have they their origin in the trans- 

 formation of carbohydrate or of protein ? 



It was once thought that in some plants fats were direct 

 photosynthetic products ; Vaucheria was the prominent 

 example amongst the lower plants and of the higher plants 

 those showing elai'oplasts were quoted. As has been mentioned, 

 there is some doubt regarding the composition of the fat-like 

 body occurring in Vaucheria f and on the available evidence 

 it is impossible to draw a definite conclusion. 



* Vol. I., p. 34. See also Terroine : " Ann. Sci. Nat. Bot. ( " 1919, 

 ser. x., I, i. 



f See Terroine, Trautmann and Bonnet : " Compt. rend.," 1925, 

 180, 1 181 ; " Bull. Soc. chim. biol.," 1925, 7, 461. 



% See Vol. I., p. 35. 



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