INFLUENCE OF THE NERVOUS SYSTEM ON SECRETION. 313 



produces contraction of the vessels of the gland and arrests secretion, while a 

 stimulus applied to the chorda tympani increases the circulation and excites 

 secretion (Bernard). Enough is known of the nervous influences which 

 modify secretion, to admit of the inference that all the glands are supplied 

 with nerves through which certain reflex phenomena, affecting their secre- 

 tions, take place. 



As. reflex phenomena involve the action of nerve-centres, it becomes a 

 question to determine whether any particular parts <5f the central nervous 

 system preside over the various secretions. Experiments showing the exist- 

 ence of such centres are not wanting, but it will be more convenient to treat 

 of these in connection with the physiology of the individual secretions. 



Mental emotions, pain, and various conditions, the influence of which 

 upon secretion has long been observed, operate through the nervous system. 

 Many familiar instances of this kind are mentioned in works on physiology : 

 such as the secretion of tears ; arrest or production of the salivary secretions ; 

 sudden arrest of the secretion of the mammary glands, from violent emotion ; 

 increase in the secretion of the kidneys or of the intestinal tract, from fear 

 or anxiety ; with other examples which it is unnecessary to enumerate. 



Paralytic Secretion by Glands. The effects of destruction of the nerves 

 distributed to the parenchyma of some of the glandular organs are very re- 

 markable. M tiller and Peipers destroyed the nerves distributed to the kidney 

 and found that not only was the secretion arrested in the great majority of 

 instances, but the renal tissue became softened and broken down. Ber- 

 nard found that animals operated upon in this way died, and that the tissue 

 of the kidney was broken down into a fetid, semi-fluid mass. After division 

 of the nerves of the salivary glands, the organs became atrophied, but they 

 did not undergo the peculiar putrefactive change which was observed in the 

 kidneys. The same effect was produced when the nerves were paralyzed by 

 introducing a few drops of a solution of curare at the origin of the little 

 artery which is distributed to the submaxillary gland. It is possible that 

 other glands have so-called motor-nerves, stimulation of which excites secre- 

 tion, but such nerves have been most satisfactorily isolated and studied in 

 connection with the salivary secretions. When the motor-nerves of the sali- 

 vary glands are divided, in the course of a day or two, the secretion becomes 

 abundant and watery, losing its normal characters. After about eight days, 

 the secretion begins to diminish and the glands undergo atrophy. The in- 

 creased secretion first observed has been called "paralytic." The watery 

 secretion discharged from a permanent pancreatic fistula is thought to be 

 paralytic ; and certainly it does not present the physiological properties of 

 normal pancreatic juice. 



Anatomical- Classification of Glandular Organs. The organs which 

 produce the different secretions are susceptible of a classification according 

 to their anatomical peculiarities, which greatly facilitates their study. They 

 may be divided as follows : 



1. Secreting membranes. Examples of these are the synovial mem- 

 branes. 



