i68 THOMPSON YATES LABORATORIES REPORT , 
Allied to the above examples is the following : — Excitation of the central end of the 
aflFerent root of the Vllth cervical nerve at times provokes extension at the elbow, but more often 
flexion ; when extension is obtained, the flexors lie absolutely without active contraction, and if 
in tonic rigidity at the time are, inhibited, actively relaxed. The two effects, namely, reflex 
flexion of elbow and reflex extension of elbow, sometimes succeed each other in the course of 
repetition of excitations even in the same few minutes. The condition indicates the incom- 
patibility of the contraction or pressor action (augmentor action) of the two groups of muscles 
under spinal reflex action : if one group is selected for increased (augmented) action the other is 
left severely alone, or if tonic contraction be going on in it, it is subjected to depression of action 
(inhibition). The carrying out of a movement by the overpowering of the active contraction of 
one muscle-group by the active contraction of another muscle-group is, throughout my experience, 
foreign to the tactical mechanism of the spinal cord. This experience harmonizes in part with an idea 
put forth some years ago by H. Munk,* and made the subject of a research undertaken at his 
instigation by ScHLOEssER.t In short, my observations prove the existence of ' reciprocal 
innervation' of antagonistic muscles as part of the machinery of spinal reflexes, and point to it as 
possibly a widely extensive part of that machinery. It not only affects contrasted muscle-groups, 
but also contrasted parts of one and the same muscle, as in quadriceps ext. fern, and in triceps brachii. 
Phasic Variation in the Reflex Activity of the Cord 
Although, as the ' rule of monotonous repetition ' above states, absence of variation of the 
movement elicited by repetitions of a particular stimulus is a striking character of spinal reflexes in 
the Mammal, and lends to them a machine-like quality of regularity, there does occur a curious 
variety of result when they are exammed in the same individual from day to day. The very spot 
of skin that one day evokes constantly flexion of all the toes, may the following day evoke nothing 
but flexion of hallux and extension of the other toes, and the day following may evoke nothing, or 
again, only the movement obtained three days before. A stimulus usually eliciting dorso-flexion 
at ankle, may on some days elicit in the same individual, plantar flexion of ankle. As a broad 
rule, it is certain that spinal reflexes are more easily elicited when a well-nourished animal is 
hungry and expectant of food, and less easily after a heavy meal. Altogether apart, however, from 
feeding time on some days, hardly a reflex can be elicited from the very animals that on other days 
yield a variety with readiness. Condition of individual age, and especially of general nutrition, 
influence, as Freusberg points out for the lumbo-sacral reflexes of the Dog, the facility of reflexes 
very greatly indeed. 
[Post-scriptum, June, 1898. — I seize a final possibility afforded to append a brief sentence 
of mention and appreciation of the admirable work of Bolk just appearing (< Morpholog. Jahrbuch,' 
vol. 25, 4, p. 465, 1898 ; vol. 26, I, p. 91, 1898), on the morphological portion of the subject- 
matter of this paper. Had the dates permitted, I should have amplified the text by collating in it 
the results he obtains in Man with those to which I have come in Macacus. His labours perform 
« ' VerhaniUungen tier Berliner Physiologischen Gesellschaft,' October, 1881. 
t 'Archiv f. Physiologic,' Du Bois-Reymond, Berlin, 1880. 
