720 PHYSIOLOGY 



fluid, e. g. water, from the blood vessels, and the transudation thus evoked 

 will be greater than that necessary to provide the water of the saliva, and 

 will therefore produce a distention of the lymphatic spaces of the gland and 

 an increased discharge of lymph along its efferent lymphatics. As a second- 

 ary result of the activity, perhaps in consequence of the removalof the 

 products of the resting metabolism of the gland, there is increased growth of 

 protoplasm, increased activity of the nucleus, and therefore a tendency to 

 increased assimilatory changes and a preparation of the cell for further 

 secretory changes either immediately or hereafter. 



In the gland as in muscle, when we attempt to form a conception of the mechanism 

 of the chemical machine in the living cell, we are brought up against insuperable 

 difficulties. One might perhaps conceive of the secretory granules being bounded by 

 a membrane impermeable to intermediate metabolites and salts, but permeable to. 

 carbon dioxide. If the first effect of stimulation of the secretory nerves were to pro- 

 duce an explosive disintegration of the complex molecules making up the granules, 

 we should have a sudden multiplication of molecules within the granules. This would 

 cause a large rise of the osmotic pressure in these granules and the consequent absorp- 

 tion of water from the surrounding protoplasm. This process however could only 

 result in the production of a fluid in the granules having the same osmotic pressure 

 as the surrounding medium, whereas we know that saliva has a molecular concen- 

 tration which is only one-half that of the blood or lymph. We should therefore 

 have to make a second assumption, namely, that, before the extrusion of the solution 

 from the granules, there is a further breakdown of the metabolites by a process of 

 oxidation, with the production of carbon dioxide which diffuses into the surrounding 

 protoplasm. We have however no evidence of either of these processes or for any 

 of these assumptions, and I have only adduced them in order to show how far we are 

 still from the actual comprehension of the events occurring in every living cell, and 

 underlying its conditions of rest and activity. 



