SECT. 7] OF EMBRYONIC DEVELOPMENT 985 



hypothetical as regards magnitude. At present there does not seem 

 to be any way of measuring the O.E. directly, but a word may be 

 said about certain attempts at doing so which have been made in 

 the past. 



In the first place, it has been argued that if any energy is bound 

 up with structure or organisation, this energy ought to be liberated 

 when the structure or organisation is destroyed. Accordingly from 

 time to time attempts have been made to discover the thermal effect 

 of death, and of these the most recent and successful is that of 

 Lepeschkin who killed yeast-cells in various ways as instantaneously 

 as possible and measured the extra heat eliminated. It worked out 

 at 2 cal. per gram of dry weight. If this energy may be in any way 

 regarded as O.E. or the equivalent of O.E. then it might be expected 

 to be rather greater in a metazoal, i.e. more heterogeneous, population 

 of cells, such as the avian embryo, but even so could not exceed 

 20 gm. cal. in the finished chick. This amount would appear as a line 

 rather than a solid block in Fig. 259. Rychlevska has also some rele- 

 vant information obtained by combusting tissues without preliminary 

 drying. 



Secondly, there is the notion that the O.E. could be found by 

 estimating the work required to stop its formation. Under the head 

 of osmotic pressure, we have already had occasion to examine the 

 work of Spaulding and of Vies & Dragoiu on the "travail osmotique 

 d' arret" of cell-cleavage. Arguing in exactly the same way, Faure- 

 Fremiet, Henri & Wurmser determined the amount of radiant energy 

 required to stop the segmentation of Ascaris eggs. An exposure to 

 ultra-violet light of wave-length 2800 A. sufficed. Thus 12-10^ ergs 

 per square centimetre were required to stop development, and the 

 receiving surface of the egg was 2-3 . lO"^ sq. cm., so that the quantity 

 of energy received by an egg and sufficient to block its development 

 was equal to: 



12 . 10^ X 2-3 . 10-^ = 12 X 2-3 = 27 ergs. 



Faure-Fremiet contrasted this value with the value for work done 

 during the whole of development calculated from his Ea. results. 

 Thus 280 cal. X 4-18 . 10^ ergs = 1 1-6 . 10^ ergs per gram dry weight, 

 and, as the specific gravity of^ Ascaris eggs is i-o8 and their diameter 

 82/Lt, the average weight of one egg must be 3-11 . 10-^ gm. During 

 the development of one Ascaris embryo, then, 503 . lO"^ cal. or 2100 



63-2 



