TRANSACTIONS OF SECTION D. — DEPT. ANATOMY AND rilYSIOLOGT. 573 



network which has been so beautifully demonstrated by recent researches, and 

 especially by those of Professor Klein ; or, again, upon the fact, proved by tlie 

 analyses of Professor Pfliiger of the gases of the saliva, that there is diu-ing secre- 

 tion great production of 00,,. as shown by the amount of this gas in the sali\a 

 behig much greater than in the blood, and upon the fact of the remarkable diffusibility 

 of acid solutions. 



Reasoning upon a large number of facts, which I have not time to refer to. 

 Professor Ileidenhain has come to the conclusion that, quite apart from the nerves 

 which control the vascular supply to a gland, there exist two distinct sets of nerve- 

 fibres in relation to the glandular elements. The first of these, which he terms * secre- 

 tory,' when stimulated, lead to the secretion of water and saline constituents; the 

 second, which he terms ' trophic,' influence the transformations of the protoplasm 

 of the cell, and thus attect the organic constituents of the secretion. 



I do not wish to pronounce a definite opinion concerning this hypothesis, but 

 would remark that the nomenclature proposed by Heidenbain appears to me to be 

 an unfortunate one, especially because it attaches a new meaning to a word which 

 had previously been used by physiologists in a different sense. I refer to the 

 adjective trophic, which has always implied ' governing nutrition.' It appears to me 

 almost inconceivable that if there exist two sets of secretorv nerves, the action 

 of each should not profoundly affect the nutrition of the cell protoplasm, though, 

 of course, it is conceivable that they should do so in very different manners. 



General Conclusions. 



The complicated studies, of which I have attempted to give you a brief sketch, 

 have led to our forming certain clear general conceptions in reference to the process 

 of secretion. They have brought into greater prominence the dignity, if I may iise 

 the expression, of the individual cell. The process of secretion appears as the 

 result of the combined work of a large number of these units. Each, after the 

 manner of an independent organism, uses oxygen, forms CO.,, evolves beat, and 

 derives its nutriment from the medium in wliich it lives, and performs chemical 

 operations of which the results only are imperfectly known to us, and which 

 depend upon peculiar endowments of the cell protoplasm, of which the causes are 

 hidden from us. So long as the protoplasm is living, the gland-cell retains its 

 power of discharging its f\mctions, and in many cases does so, so hjiig as the inter- 

 cellular liquid furnishes it with the materials required. In some cases, however, 

 the gland-cells are specially sensitive to a variatiou in the composition of the 

 nutrient liquid, certain constituents of which appear to stimulate the protoplasm 

 to increased activity. In the higher animals the cells, particularly in certain 

 glands, are in relation to nerves which, when stinudated, affect in a remarkable 

 manner the transformations of their protoplasm, leading to an increased consump- 

 tion of oxygen, an increased production of carlxmic acid, an increased evolution oT 

 heat, and an increased production of those matters which the cell eliminates aud 

 whicli constitute its secretion. 



This historical survey of the growth of our knowledge of the process of secre- 

 tion exhibits the characteristic features of biological advancement. Comparative 

 anatomy has been the foundation of, observation of facts and physical experiment 

 the road to, physiological research. At various stages the value of hypotheses has 

 been well illustrated, and, whenever they have had to make way for the broader 

 and truer interpretations suggested by the accumulation of facts and greater pre- 

 cision of observation, it has been demonstrated that the process of observation is 

 not one of simple sight but of comple.x ratiocination. 



