SECT. I] PHYSICO-CHEMICAL SYSTEM 335 



Thus for 2 c.c. of potassium chloride solution, 0-3 c.c. of distilled 

 water had to be added to get coagulation, but to 2 c.c. of KSCN 

 solution, as much as 6-4 c.c. The cations went as follows: 



Ca > Mg > Sr > K and Na. 



The egg-white of the dogfish egg was thought by Brande in 1810 

 to be identical with the jelly surrounding the egg of the frog, but 

 whether the former really consists of mucin and not albumen cannot 

 be definitely stated, for no work has since been done on it. However, 

 my wife and I, in our work on the eggs oi Scyllium canicula, frequently 

 observed a coagulation of the egg-white with acetic acid, which would 

 point to the latter possibility. 



The proteins of the echinoderm egg have never been properly 

 investigated. Vies, Achard & Prikelmaier have estimated from cata- 

 phoresis experiments that the average isoelectric point of the Para- 

 centrotus lividus egg-proteins lies between 5-0 and 5-8 pH., but their 

 grounds for this figure are not free from criticism. 



Vies & Gex, in some interesting experiments, have studied the 

 normal unfertilised sea-urchin's tgg spectrophotometrically. The 

 absorption spectrum of the normal egg has peaks or bands at 

 wave-lengths of 490, 395, 370, 315, and 230 Angstrom units, and a 

 marked trough between 260 and 240 A. This curve is very peculiar, 

 for on the one hand it shows much transparency in the ultra-violet 

 although most organic substances do not, while on the other hand 

 there is nothing at all corresponding to the bands of absorption 

 about A 275 which all proteins give. This absorption is brought 

 about by the cyclic amino-acids in the protein molecule, and it is 

 quite impossible that these should be altogether absent from the 

 egg-proteins of the sea-urchin. Vies & Gex considered various 

 technical possibilities which might explain these effects, but did 

 not think that any of them would account for what was perhaps the 

 most remarkable part of the investigation, namely, the finding that 

 on cytolysis ("white") a perfectly definite and clear absorption 

 spectrum for protein revealed itself In the intact egg, then, this 

 must be masked by something else. Speculation on the nature of 

 this mechanism would be easy, for all kinds of eflfects might be 

 responsible, e.g., formation of complexes, reduction equilibria, and 

 satisfaction in vivo but not in vitro of residual valencies in the protein 

 molecule. If this very interesting work should lead in the future 



