2l6 HANDBOOK OF PHYSIOLOGY -^ NEUROPHYSIOLOGY I 



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FIG. I. Bain's modification of the original experiment performed by Loevvi in 1921. The diagram 

 represents a reservoir of salt solution from which there is a passage to the donor heart (D); pressure 

 trom the reservoir assures a continuous flow of the solution through that heart to the recipient heart 

 (R). The donor heart still has its proper nerves. Each heart is attached to a writing lever. The record 

 is that of the two hearts, donor and recipient. When the vagal fibers of the donor were stimulated (S), 

 there was a prompt arrest of that heart (D), and later a slowing and arrest of the recipient heart 

 (R), with gradual recovery. Time (T) is recorded in 5-sec. intervals. [From Bain (7).] 



FIG. 2. Rise of arterial pressure and increase of heart rate from 

 196 to 220 beats per min. following stimulation of the hepatic 

 nerves in the cat. Time, 5 sec. [From Cannon & Uridil (21).] 



sure (fig. 2). It did not dilate the pupil, howexer, 

 which would have been expected if the substance 

 carried by the blood were epinephrine. 



The principle of chemical transmission was later 

 greatly developed chiefly by the work of Cannon & 

 Rosenblueth and their associates, and by Dale, 

 Feldberg, Minz and their co-workers. A very useful 



distinction was introduced by Dale (27) when the 

 tcrins adrenergic and cholinergic nerves were coined 

 (fig. 3). While acetylcholine still holds the position 

 allotted to it since 191 4 as the cholinergic chemotrans- 

 mitter, the concept of epinephrine as adrenergic 

 transmitter has had to yield to its nonmethylated 

 homolosiue norepinephrine (124). The "curiously 

 anomalous" effect on the iris observed by Cannon & 

 Uridil in 1921 (21) i:)ecame readilv explained by the 

 recognition that norepinephrine and not epinephrine 

 was the mediator of adrenergic nerve action. 



For a detailed account of the problem of autonomic 

 neuroeffector transmission the reader is referred to the 

 monographs of Gaddum (50), Cannon & Ro.scn- 

 blueth (20), Muralt (133), Rosenblueth (113) 

 Minz (96, 97), Euler (129) and the recent survey of 

 neurochemistry (loi). 



.^N.ATOMIC.^L CONSIDER.ATIONS 



As in other tields of ph\siolog"y, valuable hints may 

 be gained by studying the microarchitecture of the 



