SECRETION 



359 



caffeine, etc., may have a paralytic effect on the absorption by the tubules. We 

 have seen above that, although an animal may be deprived of chlorides in the food, 

 the blood continues to preserve nearly its normal concentration (0*7 per cent.) in 

 sodium chloride, while the urine may contain as little as OO8 per cent., owing to 

 the almost complete reabsorption of this important salt by the tubules. Under 

 these conditions, if one of the diuretic drugs referred to be administered, the 

 amount of the urine is increased and the sodium chloride goes up to 0-64 per cent., 

 as shown by Pototsky (1902). Such an increase is considerably greater than 

 would be accounted for by the lessened absorption of sodium chloride .011 account 

 of the more rapid passage along the tubules. 



An interesting specific diuretic action is exerted by a hormone formed by the 

 pituitary gland, as described by Magnus and Schiifer (1901) and by Schiifer and 

 Herring (1906). Extracts of this organ cause a rise of blood pressure together 

 with vaso-dilatation of the kidney and increased flow of urine. The diuresis and 

 kidney dilatation last longer than the rise of general blood pressure, so that there 

 must be a specific effect on the kidney itself. The fact is suggestive in connection 

 with the view taken by Gaskell (1908, pp. 215 and 321) of the origin of the 

 pituitary body from the coxal glands of the invertebrate ancestor, which were 

 excretory in function and remain the chief excretory organ in Limulus. One is 

 reminded also of the effect of saliva in producing activity of the submaxillary 

 gland, as described by Demoor (1913)'. 



Some special products of secretory activity may be referred to briefly in order 

 to show the great variety of products which different organisms are able to 

 manufacture. 



Acid and Alkali. In the large mollusc, Dolium galea, a kind of salivary gland 

 exists, which produces sulphuric acid of the strength of 4 to 5 per cent. (Preyer, 

 1866), apparently used for attacking the calcareous shells and spines of starfish, 

 and other echinoderms used as food. The same purpose is probably served by the 

 large percentage of aspartic acid produced by some related molluscs. It seems 

 desirable that the fact of secretion of 5 per cent, sulphuric acid should be re- 

 investigated. 



The production of hydrochloric acid in the stomach, of decimolar or even 

 higher concentration, has not yet received a satisfactory explanation. It is clear 

 that a large amount of osmotic work must be done in the process, and it is 

 difficult to suggest a possible chemical reaction by which it might be obtained 

 under the conditions compatible with cell life. Miss Fitzgerald (1910) gives some 

 hypotheses on the question. In a mixture of chlorides and acid phosphates, 

 there will be present both H' and Cl' ions, so that if the cell membrane is 

 permeable to these and not to other ions of the cell contents, it seems possible 

 that the secretion may be explained/ 



A theory has been suggested by Koeppe (1900) on the hypothesis that the gland membrane 

 is impermeable to Cl' ions and permeable to H' and Na - ions, but experimental facts obtained 

 by Benrath and Sachs (1905) do not support the view. 



The fact of the production of an acid reaction when an electro-negative colloid, 

 such as arsenious sulphide, is thrown down by neutral salts of barium, etc., as 

 mentioned above (page 94), may have some connection with the phenomenon. It 

 is, perhaps, most likely that the surface action of colloids may ultimately afford 

 a satisfactory explanation, when taken in connection with special arrangements of 

 the cell membrane as regards permeability. 



Similar remarks apply to the production of a secretion of alkaline reaction, such 

 as the pancreatic juice. 



The cuttle-fish, Sepia, as is well known, produces an inky fluid to cover its 

 retreat from enemies. The pigment contained in this secretion is used by artists 

 as a pleasant warm black or brown paint. It is one of those black or brown 

 compounds known as melanins, and, according to von Fiirth (1903, p. 372), is 

 formed in the cuttle-fish by the action of an oxidising enzyme, tyrosinase, on tyrosine. 



