436 ELECTRO-PHYSIOLOGY CHAP. 



If the claw-nerve is now tetanisecl (the demarcation current 



having been previously compensated), the usual effect with the 



gradual approximation of secondary to primary coil is a more 



or less considerable deflection in the direction of a positive 



variation of the demarcation current, followed by a diphasic 



(negative followed by positive), and finally by a simple negative 



deflection. As a rule the positive deflections are ^smaller than 



the negative deflections. With regard to the time-relations of 



the positive variation, it may be remarked that the variation, 



as a rule, follows close upon the commencement of excitation, 



and very gradually diminishes during its course. Owing to the 



fact that the adductor muscle is frequently in a more or less 



pronounced state of tonic contraction (which, as will be shown 



later, may be abolished by weak excitation of the nerve, whereas 



strong excitation always augments, or initiates contraction), it 



seems natural to bring the galvanic changes into direct causal 



relation with the simultaneous alterations of form in the 



muscle. No such parallelism of the two orders of excitation 



effects can, however, be predicted. It frequently appears that 



the electrical effect is still purely positive, or diphasic, while 



the muscle is already in tetanus. Nor is it rare to find 



cases in which the adductor muscle contracts vigorously 



with a certain strength of excitation, while the electrical' 



changes are quite insignificant, there being either a visible 



antagonism of effects, or no perceptible result, positive or 



negative. In such cases, strong currents, as a rule, produce 



negative deflections in one direction only, usually insignificant 



in magnitude, and followed by a strong positive after-effect when 



the excitation is over. Minimal galvanic effects, or complete failure 



of action, frequently occur in animals which have been exposed 



for some time to a very low temperature (0-5 C.) In other 



cases, under the same conditions, the positive variation is well 



marked and vigorous. On the whole, the experimental results 



obtained vary to a surprising extent in different, though apparently 



similar, crabs. In single cases it was found possible to obtain 



positive effects in one direction only, with any given strength of 



excitation after very strong doses of curare, although the muscle 



goes into tetanus after each stronger excitation, so that there is 



no question of complete curare effect. After poisoning with 



curare the positive variation is always strongly developed in 



