CIRCULATORY FACTORS 29 



becomes paler, the blood flow is lessened, showing that a vaso- 

 constriction has occurred. 



Circulatory Factors. That the character of the secretion is not 

 entirely due to the changes in the amount of blood flowing to 

 the glands is shown by the following facts: 



1. The blood flow may be cut off entirely when stimulation 

 of the chorda tympani still gives a secretion. 



2. Injection of atropine produces an increased flow of blood 

 but no secretion, upon stimulation of the chorda. 



3. Injection of hydrochlorate of quinine gives a vascular 

 dilatation, but no secretion until the nerve is stimulated. 



When the chorda is irritated with shocks of increasing in- 

 tensity, it is found that the amount of water and salts secreted 

 increases proportionately to a maximum limit, which for salts 

 is about 0.77 per cent., no matter what the condition of the 

 gland may be. The production of organic constituents soon 

 reaches a maximum and then declines, and is closely dependent 

 upon the previous condition of the gland. In order to explain 

 these facts, Heidenhain decided that there were two sets of 

 nerve fibers, one of which regulated the formation of organic 

 substances (trophic fibers), and the other of which regulated 

 the production of water and salts (secretory fibers). More- 

 over, their arrangement was such that the chorda carried a 

 greater number of secretory, while the sympathetic carried 

 more trophic fibers. Langley has recently offered a simpler 

 explanation of the facts, attributing the differences of the 

 chorda and the sympathetic saliva to the variations in the 

 quantity of blood supplied, so that the assumption of only 

 one kind of secretory nerve fiber is necessary. 



Section of the chorda tympani produces after a few days 

 a slow, continuous secretion for five or more weeks, when it 

 ceases. This is called paralytic secretion. Antilytic secretion 

 is the production of a flow by the corresponding gland on the 

 opposite side, the nerves of which are still intact. Section 

 of the cervical sympathetic causes a temporary dilatation of the 

 bloodvessels, but has no other effect. Atropine prevents the 

 secretion of saliva by destroying the endings of the cerebral 

 fibers in the gland, leaving, when proper doses are used, the 

 sympathetic fibers still capable of functioning. Pilocarpine 

 has an antagonistic action to atropine, causing a continual 



