276 THEORY OF SECEETION. [BOOK n. 



of the latter languishing as the storage increases. Then generally 

 as the result of stimulation, changes takes place in the cell 

 by which the zymogen is converted into actual ferment, and this 

 ejected from the cell. This is the process which we sometimes 

 speak of as the act of secretion, and it obviously has many 

 analogies with a muscular contraction. Coincident with the dis- 

 turbances which thus give rise to the ejection of ferment, the 

 constructive metabolism of the cell is excited to greater activity, 

 and for a while there is an accumulation of new protoplasm in 

 great excess of zymogen. Soon, however, but slowly rather than 

 suddenly, this new protoplasm again breaks down into zymogen, 

 which in turn is stored up in the cell, and so the cycle is completed. 



Such may be considered the more common mode of procedure ; 

 and in such a case we are enabled, as in the pancreas or mucous 

 gland, to watch the accumulation and disappearance of the zymo- 

 gen or mucigen, because this is alternately in excess of or less 

 than the actual protoplasm. But we can easily imagine .a case in 

 which all the various stages of the upward and downward 

 metabolism keep pace with each other, in which for instance when 

 any quantity of zymogen is converted into ferment which leaves 

 the cell, just that quantity of zymogen is replaced by a destruction 

 of protoplasm, and a new quantity of protoplasm appears just 

 sufficient to replace the old which has been broken down. In 

 such an instance of continuous changes it would be impossible, with 

 our present means at least to trace out the series of events, though 

 those at bottom would be identical with those where the changes 

 were discontinuous. And indeed it is obvious that this same plan of 

 secretion, if we may so call it, might be made to produce very 

 varied results, by variations in the proportions and rates of the 

 several steps. 



Admitting, however, ihis view of what we may call the proto- 

 plasmic aspect of secretion, another feature has to be considered. 

 The juice secreted by any gland consists not only of the specific 

 ferments, trypsin etc. as the case may be, found only in it, but also 

 of a large quantity of water, and of various saline or other soluble 

 substances common to it and other juices. And the question arises, 

 Is this water, or are these salts and soluble substances furnished by 

 the same act as that which supplies the specific constituents ? 



To this we may reply, that the very water is discharged by the 

 activity of the cell, and is not a mere filtration from the blood- 

 vessels. For, as we have seen in the case of the salivary glands, 

 when atropin is given, not only do the specific constituents cease 

 to be ejected in spite of the vessels becoming dilated, but the 

 discharge of water is also arrested: no saliva at all leaves the 

 gland. And what is true of the salivary glands probably holds 

 good with the other glands. Assuming then that even the escape 

 of water is the result of the activity of the cell, we cannot but feel 

 an increased interest in the fact mentioned some time ago, that in 



