SECT. l] 



PHYSICO-CHEMICAL SYSTEM 



333 



not easy to see why Valenciennes & Fremy did not identify it with 

 that substance. The remaining egg-proteins, which they did not 

 further investigate, they referred to under the generic name of 

 albumen. 



Table 35. Investigations 



AvES Callus domesticus 



Pisces 



of Valenciennes & Fremy. 



Vitellin 



The differences between the compositions which Valenciennes & 

 Fremy found for these substances are not great, and it is very doubtful 

 whether they are more than modifications of the same substance, 

 especially as these workers admittedly had great difficulty in ob- 

 taining pure preparations. But the problem of the identity of the 

 vitellins is not yet settled. The later investigations are all grouped 

 together in Table 33, and the differences between the preparations 

 can easily be seen to be small. The work of Plimmer & Scott 

 proved that ichthulin is a phosphoprotein closely allied to vitellin. 

 Among the more interesting observations must be mentioned 

 those of Levene & Mandel; Levene, and Walther, on ichthulic acid 

 obtained from the ichthulins of various fish eggs by digestion 



