35 



more so than the sea-water and more so than the perivisceral 

 fluid, which both have a P H of 8.2-8.3. This acidity is strange 

 is so far as the secretion of free acid has never been shown 

 to occur in lower organisms. This is true, of course, as far as 

 the digestive juice is concerned ; the secretion of acid by sea- 

 snails etc. (Semon 119)) and analogous phenomena are not to 

 be discussed here. Even in animals as high in the scale of 

 phylogenesis as the dogfishes, it has not yet definitely been 

 settled whether free acid actually is present or not. In a 

 controversy between Wei nland and Miss van Herwerden 

 see van Herwerden 56), Wei nland 132), and van 

 Herwerden and Ringer 57) the former author has been 

 critisising the S j 6 q v i s t method for determination of free acid, 

 used by Miss van Herwerden, as not being reliable if 

 earth-alcalies are present. Van Herwerden and Ringer 

 have answerred that the PH 1 .69 which is the same as that 

 of 0.02 N acid and given many other arguments in favor of 

 the presence of free acid. 



Yet the acidity of the digestive juices in our group must have 

 a cause of some sort and maybe a chemical investigation of the 

 digestive fluid will furnish us some information. Since the ma- 

 terial was not available in large quantities, I had to run my 

 tests microchemically. A certain quantity of the digestive juice 

 was secured ; separate drops were used for the tests to which 

 small quantities of the reagents were added from capillary tubes. 



All the tests gave the same result in the digestive juices of 

 Arbacia and Thyone. For this reason I do not treat these two 

 species separately. 



The first possibility to be thought of, is the presence of phosphates. 

 They are present in large quantities in the gut of Tenebrio, 

 where a weakly acid reaction has also been found ! ). These 

 acid (dihydrogen-) phosphates can, if magnesia is present at the 

 same time, be demonstrated very easily by a white crystalline 

 precipitate of ,,tripel-phosphate" formed after the addition of am- 

 monia. They are absent however in the digestive fluid of the 

 snails and do not seem to be present either in our Echinoderms. 



Ammonia did in fact give a precipitate. But this precipitate 

 was probably nothing but simply calcium hydroxyde since it did 

 not have the typical appearance of the ,,Tripelphosphat". Other 

 tests were equally negative, Mg-mixture did not give any preci- 

 pitate, with Ur-nitrate a very slight precipitate was obtained. 

 This might indicate that a trace of phosphates is present, but 

 at the same time, that this quantity must be very small. 



An ammoniacal solution of ammonium oxalate gave a heavy 



l ) A fluid behaving chemically just like the digestive juice of these animals, 

 could be obtained by adding a trace of ammonia to a solution of mono- 

 sodium phosphate. 



