THE FUNCTIONS OF THE DIGESTIVE ORGANS. 491 



Besides this secretion the animal empties from its pharynx a very strongly- 

 acid-reacting juice. This comes from a gland-like structure consisting of 

 long coils enveloped in a highly complicated, contractile network. The 

 chief constituent of the individual cells is a liquid, while the amount of pro- 

 toplasm itself is relatively small. If the gland is stimulated, the above- 

 mentioned network contracts; and the liquid secretion of the gland-cells, 

 which is contained in larger or smaller vacuoles, is emptied into the 

 exit duct. Evidently in this case the secretion is merely mechanically 

 removed from the cells. After the relaxation of the contracted cell-coil, 

 there remain in the cells at first only the shrunken protoplasm and the 

 cell-nuclei, and then begins anew the formation of secretion. Several 

 things indicate that the nucleus itself plays an important part in this 

 process. The secretion contains free sulphuric acid. What is the source 

 of this acid? It might come from sulphates, or from organic compounds 

 containing sulphur, such as, for example, albumin. The latter is hardly 

 to be considered as a possible source of sulphuric acid. It seems certain 

 that most of the acid must be formed from sulphates, for the amount of 

 acid produced is too large, and the amount of sulphur present in albumin 

 too small, to account for the formation by the assumption of an oxidizing 

 decomposition, as, for example, of cystine. It has been found that the 

 secretion continues during starvation. If the albumin itself were the 

 source of the sulphur, we would expect that the formation of sulphuric acid 

 would soon cease in the starved organism. It has never been explained 

 how the cells in the gland are able to produce the free acid. When we come 

 to discuss the formation of hydrochloric acid in the human stomach, we 

 shall find likewise that we are again in the dark. It has been attempted 

 to explain the formation of the strong acid as a result of the mass-action 

 law. We know that from salts of the mineral acids a small amount of 

 acid may be set free by the action of large amounts of carbonic acid, for 

 example. We also know that as a result of ionization a small amount of 

 acid ions are probably set free in the organism. We shall not deny that 

 perhaps a part of the acid in the secretion may be formed in some such 

 way, and it is indeed conceivable that eventually all of the acid may be 

 produced in such manner, if we assume that as soon as a little acid is set 

 free, it is in some manner carried out of the range of chemical reaction, so 

 that constantly more and more of the acid will be formed. But even such 

 an hypothesis, which necessitates the further assumption of some means 

 of removing the acid as fast as it may be formed, does not enable us to 

 explain satisfactorily the whole process. At all events, the cells themselves 

 must exert a specific action. In this case, the cells of the gland form sul- 

 phuric acid alone, while in the stomach only hydrochloric acid results. It 

 might be assumed that the membrane of the cells is only permeable to certain 

 ions. It has, for example, been asserted that the walls of the stomach axe 



