32 



and used by him in his work in the M. B. L. The standards 

 were kept for about a month in Jena Erlenmeyers closed 

 tightly with rubber stoppers. 



Juice of the different parts of the gut of Thyone and of 

 Arbacia was secured. One drop was put on a white porcelain 

 plate on which a series of standard drops had been laid out 

 previously. Equal quantities of indicator were added to the 

 different samples— I used a narrow capillary tube for this purpose— 

 and the color comparison made. As an indicator I used phenol-red. 



On Thyone four sets of determinations were made. A series 

 of figures was secured for the different parts of the gut. This 

 is especially easy in these animals on account of the length of 

 their gut and because their intestine is nearly always full of 

 liquid. The results obtained in this way are represented in 

 table 3. 



Table 3. 



Hydrogen-ion concentration in Thyone gut. 



In the urchins it proved to be very difHcult to secure liquid 

 from definite parts of the gut, partly on account of the more 

 complicated anatomical relations, partly because these guts 

 usually do not contain much liquid. I obtained two series of 

 figures, but I do not give them any more value than just 

 figures of the Ph of an arbitrary drop of digestive juice. Their 

 values are represented in table 4. 



Table 4. 

 Hydrogen-ion concentration in Arbacia gut. 



