290 Prof. C. 8. Sherrington. [Apri ake 
Thus, in the ordinary “flexion reflex,” initiated, say, from the right foot, the 
flexion of the homonymous knee is easily seen to be due to contraction of 
its flexor muscles, also the concomitant extension of the crossed knee is easily 
seen to be due to contraction of its extensor muscles. But it requires special 
preparations to detect that with the contraction of the right knee-flexors 
there goes reflex inhibition of the right extensor, and that with the contrac- 
tion of the left knee-extensor there goes reflex inhibition of the left knee- 
flexors. This being so, when under strychnine the reflex is suddenly changed 
in character, both flexors and extensors being in both legs thrown into con- 
traction together, it appears to an observer, unaware of the previous 
inhibitions, that, under the strychnine, the reflex action reached muscles 
which it did not reach before, eg., right knee-extensor and left knee-flexcr. 
Hence rises the hypothesis that the alkaloid breaks down a supposed spinal 
“resistance,” previously intervening between the afferent nerves and various 
motor spinal cells ordinarily inaccessible to them. Strychnine does lower 
the threshold stimulus for spinal reflexes at one stage of its action; but the 
central fact of strychnine effect appears to me that it destroys spinal taxis 
for the skeletal musculature by upsetting the fundamental co-ordination of 
reciprocal innervation. It upsets reciprocal innervation because it transforms 
inhibition into excitation. | 
The vast 7d/e of inhibition in cerebral processes, as evidenced by mental 
reactions, and the slightness of mental symptoms in acute strychnine 
poisoning, indicates a difference between inhibition as it occurs in the bulbo- 
spinal arcs and in the arcs of purely sensual and perceptual level, a 
difference presumably of chemical nature. 
Addendum, May 15, 1905. 
At the date of the foregoing I had had opportunity for but a few 
experiments with tetanus-toxin, and those with one preparation only of the 
toxin. The results then obtained showed, as mentioned, that the toxin, as 
does strychnine, converts inhibition effect into excitation effect. I have 
since been abie to make further observations, and with two other prepara- 
tions of the toxin besides my own. For a solid preparation, I have to thank 
the kindness of Professor Roux, Director of the Institut Pasteur; for a 
fluid, Dr. Stenhouse Williams. The results yielded by each of these have 
been confirmatory of the mentions made in the Note. 
The action of the toxin in respect to inhibition resembles that of strychnine 
closely in several ways. Thus, in the stages of the disease in which the tetanus 
is still “local” and manifested in one limb, namely, that (¢y., the hind limb) 
which received the toxin injection, the toxin early converts into excitation the 
