332 THE UNFERTILISED EGG AS A [pt. iii 



Gobley on the hen's egg, which has already been described, a more 

 solid basis for comparison was achieved, and Valenciennes & Fremy, 

 in a memoir which received a prize from the Academy of Sciences 

 and which was translated into English, proceeded to examine the 

 eggs of as many species as were available to them. Gobley's only 

 excursion into comparative chemical embryology had been a detailed 

 analysis of the carp's egg, published in 1850, but he had not been slow 

 to point out the differences between this analysis and that of the hen's 

 egg. His figures are shown in Tables 2, 30 and 33, where it will be 

 seen that he got a value of 15-76 per cent, protein (wet weight) for 

 the hen, and 14-23 per cent, for the carp, but 31-43 per cent, fat 

 for the hen and only 2-57 per cent, fat for the carp. The carp's egg 

 had, he found, about 10 per cent, more water than the yolk of the 

 hen's egg, but only a third of the lipoid substances. 



Fremy & Valenciennes specially directed their attention to the 

 protein fraction, and attempted to discover whether the vitellin was 

 the same in all eggs. For the most part they relied on histological 

 appearances (the "dotterplattchen" were greatly discussed at this 

 time), but they also examined the solubility relationships of the 

 proteins from each egg, and in some cases subjected the purified 

 substances to elementary analysis. The figures they obtained for the 

 different compounds are all given in Table 33, and the eggs they 

 investigated in Table 35. They were able to isolate a number of 

 vitellin-like proteins, soluble in salt solution and precipitated 

 by the addition of water. They compared vitellin with fibrin, 

 and concluded that the two substances were almost identical, in 

 spite of slight differences in the analytical figures — "for bodies 

 of this nature", they said, "which are not crystallisable and 

 insoluble in water and which are therefore very difficult to purify, 

 where is the chemist who could answer for i per cent, of nitrogen in 

 an elementary organic analysis?" Ichthin, which they isolated from 

 fish eggs, differed from vitellin by not becoming an opaque mass 

 when placed for a long time in boiling water, and by giving a 

 violet instead of a blue colour when treated with boiling hydrochloric 

 acid. Ichthidin, another product offish eggs, differed from ichthin in 

 being soluble in water. Ichthulin, the third member of the group, 

 differed from the others in not being soluble in all dilutions of saline, 

 but in being precipitated from the aqueous extract by further ad- 

 dition of water. As for emydin, it closely resembled ichthin, and it is 



