852 GENERAL METABOLISM [pt. iii 



echinoderm eggs. For later stages the following interesting values 

 were obtained: 



Table 98. Triton taeniatus. 



pa 



Blastula External cell layer y-G-y-S 



Blastocoele liquid 8-4-8-6 



Gastrula (beginning) ... Ectoderm y-G-y-Q 



Gastrula (late) ... ... Ectoderm 7-6 



Endoderm ("Urdarm") 8-i 



Neurula ... ... ... Ectoderm cells 6-9-7-0 



Cells of neural tube 6-8 



Endoderm ("Urdarm") 8-i 



Endoderm (yolk-mass) 6-g-7-o 



An interesting research on the eggs of Arbacia was that of Vies 

 & Vellinger, who made spectrophotometric observations on the 

 pigment normally contained in these cells. This involved no inter- 

 ference with the material at all, and only required a preliminary 

 isolation of the pigment and a study of its properties in vitro. It must 

 be remembered that the behaviour of the pigment in the cell as 

 a pH. indicator may only show the hydrogen ion concentration of a 

 very limited phase, in which the indicator happens to exist. Vies & 

 Vellinger attempted to overcome some of these difficulties by com- 

 paring the colour change of the indicator (their "Arbacine" was 

 probably identical with McClendon's "Echinochrome") [a] in 

 alcoholic solution and {b) unremoved from a thawing "puree" of 

 eggs. They showed that the colour change from orange through violet 

 to yellow took place according to j&H in much the same way in the two 

 cases. By a comparison of the spectrum of the pigment when in the 

 intact cell with the various spectra of the pigment under known con- 

 ditions of />H, they ascertained that the former corresponded to a />H 

 of about 5-5, from which they concluded that this represented the pYi 

 of the cytoplasmic elements or phases where the pigment was present. 

 Spectrophotometric curves confirmed the results obtained by simply 

 looking at the spectra, save that there was evidence of two pigments, 

 one with two maxima and one with one. The pigment of the Arbacia 

 egg is known, according to the work of Heilbrunn and many others, 

 to be localised in certain definite elements. This means that what is 

 probably the best possible method of studying the intracellular 

 hydrogen ion concentration has not so far been able to give a value 

 for the inside of a cell as a whole, or for what we roughly call 

 protoplasm. It is to be feared that it will always be of less general 



