414 SECRETION. 



supply of nervous influence ; for some glands are supplied 

 with sympathetic, others, with cerebro-spinal nerves, and 

 others with both kinds ; yet the mode of secretion appears 

 to be in all alike. The experiments of Bernard, Brown- 

 Sequard, and others, however, seem to show that all 

 secreting glands are provided with two distinct orders of 

 nerves, namely, motor and ganglionic : the latter appear 

 to act by causing contraction of the blood-vessels supplying 

 the gland, and thus diminishing the secretion, the former 

 lead to dilatation of the vessels, and an abundant supply 

 of blood, whereby the secretion is augmented. This was 

 well shown in Bernard's experiments on the secretion of 

 gastric fluid, irritation of the pneumogastric increasing it, 

 irritation of the sympathetic branches of the semilunar 

 ganglia diminishing or arresting it. 



The exact mode, however, in which the nervous system 

 influences secretion, must be still regarded as obscure. In 

 many cases, it probably exerts its influence, as just said, 

 by increasing or diminishing the quantity of blood supplied 

 to the secreting gland, in virtue of the power which it 

 exercises over the contractility of the smaller blood-vessels. 

 Its influence over secretion, as well as over other functions 

 of the body, may be excited by causes acting directly upon 

 the nervous centres, upon the nerves going to the secreting 

 organ, or upon the nerves of other parts. In the latter 

 case, a reflex action is produced : thus, the impression 

 produced upon the nervous centres by the contact of food 

 in the mouth, is supposed to be reflected upon the nerves 

 supplying the salivary glands, and to produce, through 

 these, a more abundant secretion of saliva. 



Through the nerves, various conditions of the mind also 

 influence the secretions. Thus, the thought of food may 

 be sufficient to excite an abundant flow of saliva. And, 

 probably, it is the mental state which excites the abundant 

 secretion of urine in hysterical paroxysms, as well as the 

 perspirations and, occasionally, diarrhoea which ensue under 



