iii8 PROTEIN METABOLISM [pt. iii 



embryo, it may be said that it certainly uses more protein as an 

 energy source than terrestrial embryos do, whether this be expressed in 

 terms of the initial store of protein or of the total amount of material 

 catabolised. Such a rule would be expected from the composition 

 of the fish egg, which, as Greene said, has on an average 27 per cent, 

 of protein in its yolk as against the 1 6 per cent, of protein present 

 in the yolk of the chick. 



8-0 12-2 2050 0-595 



9-12. Protein Metabolism of Insect, Worm and Echinoderm 

 Eggs 



Among the insects, the egg which has received the most examina- 

 tion from this point of view is that of the silkworm, Bombyx mori. 

 Tichomirov, who studied its metabolism in 1882, observed a diminu- 

 tion of protein (estimated roughly by solubility) from 11-3 to 9-2 per 

 cent, of the dry weight, i.e. i8-6 per cent, of the original material, 

 although, as only 14-9 per cent, of the original dry weight was lost, 

 all the protein cannot have been combusted. 



In more recent times, the proteins of the silkworm egg have 

 been investigated anew by Pigorini. He divided them into several 

 fractions : (^4) proteins soluble in distilled water, albumens, (J5) pro- 

 teins soluble in 7-5 per cent, sodium chloride solution, globulins, 

 (C) proteins soluble in 0-5 per cent, sodium hydroxide solution, 

 vitellin and nucleoprotein, and finally (Z)) proteins soluble in water, 

 but incoagulable by heat, and having the property of liberating 



