592 ANNALS NEW YORK ACADEMY OF SCIENCES 



chloride, another quarternary, acts powerfully on medullated nerve 

 and so, presumably, penetrates easily. 



A seemingly crucial test has been carried out in the last few weeks 

 in our laboratory by Miss Graham. ACh Br (1 : 1000 in isotonic KCl 

 with vital red) was injected into single muscle fibers of the eserinized 

 frog sartorius with a micropipette, and the membrane potential meas- 

 ured. With one electrode inside the fiber and another outside, mem- 

 brane potentials of 40 to 80 mV are regularly obtained. Injection of 

 a large drop of isotonic KCl with or without ACh, large enough to fill 

 the fiber cross-section and spread one to three diameters along its 

 length, will immediately lower the potential by one- to two-thirds; but 

 a smaller drop, not filling the entire cross-section, has little effect; only 

 7% fall, in one fully satisfactory experiment with ACh. It seems, then, 

 that ACh inside the membrane does not depolarize it, as postulated 

 by Nachmansohn and by Beutner and Barnes. 



A number of other points have been raised here, which must also be 

 kept in mind. Bodansky has emphasized the existence of a family of 

 esterases, even in different neural structures of the same species: e.g., 

 the enzymes in cervical sympathetic ganglion and in brain show different 

 substrate and ion concentration optima, different equations relating 

 concentration to activity, different substrate selectivities, etc. The 

 last point is especially important, since a criterion urged for discrim- 

 inating between "true" and "pseudo" esterase is the relative inactivity 

 of the true enzyme with tributyrin. Yet the "true" esterase of brain 

 splits triacetin up to six times faster than it does ACh. 



The distribution of ChE or ACh, or both, in various organs and tis- 

 sues has also been mentioned by several discussants. Rosenblueth 

 asked about conduction in adrenergic nerve fibers, which lack the ACh 

 system ; Hoagland made a similar point about Nitella, which conducts 

 independently of ACh; another discussant mentioned a recent report 

 that ChE is absent in the electric organ of Malaptorurus ; and the caro- 

 tid body, although specifically sensitive to ACh, is reported to lack 

 ChE.^^ ChE is also absent from the iris sphincter of the amphibian 

 eye, while present in its cornea and in the turtle's sphincter.^* Con- 

 versely, parts of the ACh system are richly present in spleen, placenta, 

 cornea, potatoes, and some bacteria, where any relation to neural func- 

 tion is nearly, or quite, impossible. And finally, in this connection, 

 many other agents act on, and other enzymes are present in, neurones. 

 Adrenalin keeps up the action potential in isolated cat nerve ;^^ ATP 

 stimulates smooth, as well as striped, muscle ;^^ carbonic anhydrase is 

 interestingly distributed in the brain ;^^ CO2 has marked and differential 



