THE SALIVARY GLANDS 259 



given we know that this poison acts upou the end organs of the two nerves in 

 an entirely different way. Hence we can scarcely say that the sympathetic and 

 the chorda are composed of the same kinds of fibers in relatively different num- 

 bers (Langley). 



The discovery of Gerhardt with regard to morphological changes in the sub- 

 maxillary after section of the sympathetic and of the chorda, speaks to the same 

 effect. In the former case the protoplasm remains unchanged, whereas the 

 nucleus shrinks, although not in all cells; after section of the chorda the nu- 

 cleus remains normal, but the protoplasm in many cells undergoes significant 

 changes, becoming turbid, finely granular and opaque. 



A further difficulty for Heidenhain's theory is the so-called paralytic secre- 

 tion discovered by Cl. Bernard. Some twenty-four hours after section of the 

 cerebral nerves, the submaxillary gland begins to secrete, slowly at first, then 

 faster and faster until within a week a drop issues from the duct every twenty 

 minutes. It makes no difference whether the sympathetic is injured or not; 

 section of this nerve produces no paralytic secretion. In the course of time 

 after section of either nerve the size of the gland gradually diminishes, and 

 the gland acquires a waxlike appearance. 



A priori it might be supposed that secretion is only a process of filtration 

 from the blood through the capillary walls. But we have great difficulty on 

 such an hypothesis to account for the chemical properties of the secretion; 

 for several substances found in the secretion and in the glands are not found 

 at all in the blood, and must, therefore, be formed in the gland cells. This is 

 attested also by facts to be discussed later with regard to morphological changes 

 appearing in the glands. But more convincing is the following. If the duct 

 of the submaxillary gland be connected with a Hg-manometer and the cerebral 

 nerve be then stimulated, the mercury in a very short time, even within twenty- 

 five seconds, rises 100 mm. higher than the mercury in a manometer connected 

 with the carotid. That is, the secretion pressure becomes higher than the 

 blood pressure. Finally, the remotest possibility of regarding the secretion 

 as a process of filtration is excluded by the fact that stimulation of a secretory 

 nerve causes a flow of saliva in animals which have been bled to death. 



When a nerve is stimulated, the constituents already deposited in the 

 gland cells during rest are not only given off, but there is at the same time 

 an increased production of them. This is plainly indicated by the fact that 

 the quantity of nitrogen in both the secreting gland and its secreted saliva is 

 greater than that of the resting gland on the other side (Pawlow). When 

 the nerves are excited with stimuli of increasing strength, not only does the 

 absolute quantity of the secretion and of its solid constituents increase, but 

 the percentage content of the latter rises higher the more rapid the rate of 

 secretion becomes. This increase always affects the inorganic constituents, 

 but not the organic, unless care be taken not to fatigue the gland by over- 

 work. If the gland be fatigued, the percentage content of organic substances 

 may even decline in the face of an increased rate of secretion. 



We may summarize the effects produced in the glands by stimulation of 

 their nerves as follows : ( 1 ) A change takes place in the gland cells develop- 

 ing certain forces which are expressed by the act of secretion; (2) at the 

 same time an increased formation of the specific constituents of the secretion 

 appears; and (3) if the stimulation continue for a long time, the gland gradu- 

 17* 



