SECT. II] FAT METABOLISM 1189 



Tangl & Farkas' hypothesis nor Gortner's experiments throw any Hght 

 on the origin of the synthesised fat in these eggs. Apparently the only 

 reason why Tangl & Farkas suggested a glucoprotein as the energy 

 source was because they could not imagine fat being synthesised from 

 anything else. Each egg, they found (by analysis), expended 6-68 cal. 

 during development, and they reasoned that to produce this energy 

 from 518 eggs (their experimental number) 1-67 gm. of glucoprotein 

 (9-7 Cal.) must be broken down to 0-38 gm. of fat (3-5 Gal.) and 

 0-30 gm. of glycogen (1-3 Gal.), and all of the nitrogen retained in the 

 form of urea (0-57 gm., i.e. 1-40 Gal.), the difference between these 

 heat values being carbon dioxide and water with a heat value of 

 3-5 Gal. As they found experimentally a heat loss of 3-46 Gal., they 

 considered that their theory covered the facts sufficiently well, but it 

 would be easy to think of several others equally convincing. They 

 found, moreover, that the loss of carbon, 46-3 per cent., did not agree 

 with the expected loss, 68 per cent., and they suggested that perhaps 

 it was not all eliminated as carbon dioxide, but retained in some other 

 form. 



The problem is undoubtedly a difficult one and at present there is no 

 solution for it, but there are two points which seem to have been over- 

 looked by all those who have so far considered it. In the first place, even 

 when the increase in "fat" has been demonstrated to be an increase 

 of fatty acids, and not of total ether extract, it has always been 

 assumed that no breakdown of these can have been occurring. Yet 

 it is possible that a catabolism of fatty acids might exist masked 

 by a reverse process, so that, as the fats were destroyed, more were 

 formed from some other source so as to over-compensate for the 

 fat combustion. The second suggestion is that substances such as 

 spinacene (see p. 350), which have recently been found in fish eggs, 

 may play a very important part as energy sources. So far there is 

 no experimental foundation for this idea, but it is quite conceivable 

 that spinacene or squalene might be oxidised directly for energy, or 

 that such substances might be the origins of the synthesised fat in 

 certain aquatic eggs. It is indeed difficult to see any biological reason 

 why this fat synthesis should go on, and it is noticeable that it never 

 reaches great dimensions — 8 per cent, in the salamander, 55 per cent, 

 in the snail (if we may trust Burdach's figures), and 5 per cent, in the 

 trout. It is true that the increase in the plaice is 264 per cent., but 

 the total quantities in question there are exceedingly small relative to 



