440 NATURE OF THE ACT OF SECRETION. [BOOK 11. 



cell-substance but eventually discharged ; and certain of the con- 

 stituents of the several secretions, such as mucin, trypsin, pepsin 

 and the like appear to be in a similar way products of the meta- 

 bolism of the cell, lodged for a while in the cell-substance, not in 

 all cases exactly in the condition in which they will be discharged 

 from the cell, but in an antecedent phase such as zymogen or the 

 like, and in all cases ultimately ejected from the cell, to supply 

 part and generally the important part of the secretion. 



239. The act of secretion itself. The above discussion pre- 

 pares us at once for the statement that the old view of secretion 

 according to which the gland picks out, separates, secretes (hence 

 the name secretion) and so niters as it were from the common 

 store of the blood the several constituents of the juice, is untenable. 

 According to that view the specific activity of any one gland was 

 confined to the task of letting certain constituents of the blood pass 

 from the capillaries surrounding the alveolus through the cells to 

 the channels of the ducts, while refusing a passage to others. We 

 now know that certain important constituents of each juice, the 

 pepsin of gastric juice, the mucin of saliva and the like, are formed 

 in the cell, and not obtained ready made from the blood. A minute 

 quantity of pepsin does exist it is true in the blood, but there are 

 reasons for thinking that this has made its way back into the blood, 

 either being absorbed from the interior of the stomach or, as seems 

 more probable, picked up directly from the gastric glands ; and so 

 with some of the other constituents of other juices. The chief or 

 specific constituents of each juice are formed in the cell itself. 



But the juice secreted by any gland consists not only of the 

 specific substances such as mucin, pepsin or other ferment, or other 

 bodies, found in it alone, but also of a large quantity of water, and 

 of various other substances, chiefly salines, common to it, to other 

 juices and to the blood. And the question arises, Is the water, 

 are the salts and other common substances furnished by the same 

 act as that which supplies the specific constituents ? 



Certain facts suggest that they are not. For instance, as 

 mentioned some time ago, in the submaxillary gland of the dog, 

 stimulation of the chorda tympani produces a copious flow of 

 saliva, which is usually thin and limpid, while stimulation of the 

 cervical sympathetic produces a scanty flow of thick viscid saliva. 

 That is to say, stimulation of the chorda has a marked effect in 

 promoting the discharge of water, while stimulation of the sym- 

 pathetic has a marked effect in promoting the discharge of mucin. 

 To this we may add the case of the parotid of the dog. In this 

 gland stimulation of a cerebro-spinal nerve, the auriculo-temporal, 

 produces a copious flow of limpid saliva, while stimulation of the 

 sympathetic produces itself little or no secretion at all ; but when 

 the sympathetic and cerebro-spinal nerves are stimulated at the 

 same time, the saliva which flows is much richer in solid and 

 especially in organic matter than when the cerebro-spinal nerve 



