SECT. I] PHYSICO-CHEMICAL SYSTEM 341 



non-protein nitrogen accounts for from 14 to 35 per cent, of the total 

 nitrogen, and one in which it only accounts for less than 10 per cent, 

 of the total nitrogen. It is evident from the work of Konig & Gross- 

 feld that all the fishes examined belong to the first of these categories, 

 although within the group there are wide divergences, such as the 

 minute amount of albumen apparently present in the trout's egg 

 and the low non-protein nitrogen of the herring's egg. Good agree- 

 ment is to be noted between the results of Levene and Konig & 

 Grossfeld, who all worked on the cod; and, although nothing con- 

 cerning the non-protein nitrogen can be gathered from the figures of 

 Kensington and Hugounenq, their results do show general agreement 

 as regards the partition of nitrogen among the proteins. The only 

 reptile on whose eggs work has been done which could be incorporated 

 in the table is the grass-snake, and there, although no non-protein 

 nitrogen figures are available, it is interesting to note the very high 

 proportion of keratin. 



Table 40. 



Silkworm (Bomfryx: mon). (Pigorini, 1Q23.) 

 In % of total protein 



A 



Protein sol. in water but not 

 Protein sol. in Protein sol. in Protein sol. in coagulable by heat, and 



distilled water 10 °„ salt sol. dilute alkalies yielding glucosamine on 



(albumen) (vitellin) (nucleoprotein) hydrolysis (ovomucoid) 



29-20 8-57 11-45 5090 



The second principal group, consisting of those eggs which have 

 a relatively much lower percentage of non-protein nitrogen, contains 

 two members, the hen and the silkworm. The former may be said 

 with a high degree of probability to be characteristic of all 

 nidifugous birds, and perhaps of nidicolous ones also, but whether 

 the latter is at all representative of the centrolecithal insect eggs 

 may be considered doubtful. The sole insect egg which has been 

 investigated chemically, so far, is that of the silkworm, and until 

 more evidence is available the hen and the silkworm will have to 

 be placed together in this second group without comment. It is 

 significant that, in the hen's case, the percentage of albumen is 

 greater than in any other, a fact obviously referable to the large 

 amount of egg-white present in that egg. Finally, it is of interest 

 that the sea-urchin's egg seems to have a protein/non-protein nitrogen 

 ratio very like that of the fishes, but situated on the low protein 

 edge of their limits of variation. 



