INFLUENCE OF NERVES ON SECRETION. 273 



These latter fibres may be called "trophic/' since they 

 directly control the cell metabolism: while the former may 

 be called " transudatory" fibres. Some of the evidence 

 which leads to this conclusion is a little complex, but it is 

 worth while to consider it briefly. In the first place, on 

 .stimulation of the chorda of an unexhausted gland (that is 

 a gland not over-fatigued by previous work) the following 

 points can be noted: 



With increasing strength of the stimulus the quantity of 

 the secretion, that is of the water poured out in a unit 

 of time, increases; at the same time the mineral salts also 

 increase, but more rapidly, so that their percentage in a 

 rapidly formed secretion is greater than in a more slowly 

 formed, up to a certain limit. The percentage of organic 

 constituents of the secretion also increases up to a limit; 

 but soon ceases to rise, or even falls again, while the water 

 and salts still increase. This of course is readily intelligible; 

 .since the water and salts can be derived continually from 

 the blood, while the specific elements, coming from the 

 gland-cells, may be soon exhausted; and so far the experi- 

 ment gives no evidence of the existence of distinct nerve- 

 fibres for the "salts and water, and for the specific elements: 

 all vary together with the strength of the stimulus applied 

 to the nerve. But under slightly different circumstances 

 their quantities do not run parallel. The proportion of 

 specific elements in the secretion is largely dependent on 

 whether the gland has been previously excited or not. 

 Prior stimulation, not carried on of course to exhaustion, 

 largely increases the percentage of organic matters in the 

 secretion produced by a subsequent stimulation; but has no 

 effect whatever on the quantity of water or salts. These 

 are governed entirely by the strength of the second stimu- 

 lation. Here, then, we find that under similar circumstances 

 the transudatory and specific elements of the secretion do 

 not vary together; and are therefore probably dependent 

 upon different exciting causes. And the facts might lead 

 us to suspect that there are in the chorda, besides the vaso- 

 dilator, two other sets of fibres: one governing the salts 

 and water, and the other the specific elements of the secre- 



