346 Prof. C. S. Sherrington. On Reciprocal [Mar. 9, 



limb are severed. A similar thing is seen with adductor minor, and with 

 quadratics femoris under appropriate conditions for their tension. Similarly, 

 under decerebrate rigidity, the tonic contraction of the vasto-crureus is 

 markedly increased by a few passive extensions and flexions of the knee ; 

 and this holds good when the only nerve unsevered in the two hind limbs is 

 that of the vasto-crureus in question. Similarly, the tonic contraction of 

 the gastrocnemius-soleus can be markedly increased by a few passive 

 extensions and flexions of the ankle, and this holds when all nerves have 

 been severed except those issuing from these muscles themselves ; the effect 

 ceases when the spinal afferent roots have been cut. 



4. On lifting a dog in which spinal transection above the lumbar region 

 has been performed, and the period of shock passed over, it is extremely 

 frequent for strong reflex extension of both hind limbs to occur. Both 

 limbs are simultaneously extended at knee and ankle. This does not occur 

 if, when the animal is lifted, the hind limbs are prevented from dropping 

 under their own weight. Passive support of the limbs, under the thighs 

 for instance, precludes the reflex. 



5. It was stated above that faradisation or mechanical compression of 

 the nerve of the vasto-crureus provokes with regularity an inhibitory 

 relaxation of that muscle and of soleus and gastrocnemius. Occasionally, 

 however, though, in my experience, quite rarely, if the nerves of the limb 

 be all of them severed, excepting only that of the vasto-crureus itself, and 

 that nerve be split into two divisions, central stimulation of one division 

 may provoke slight extension at the knee if the initial posture of the knee 

 at the time be full flexion.* But the same stimulation provokes inhibitory 

 relaxation of the extensor if the initial posture of the knee at the time 

 be fair extension. This result seems to resemble some reflex results recorded 

 by v. Uexkull in Invertebrata.f 



6. Finally, it may be recalled that various observers regard " knee-jerk " 

 and " ankle-clonus " as reflex reactions, in spite of the admitted brevity of 

 the latent time of the former. The knee-jerk is obtainable in the spinal 

 animal when all nerves of the two hind limbs have been severed, excepting 

 only the nerve of the vasto-crureus muscle in which the " jerk " is being 

 examined.^ It then ceases at once on severing the afferent spinal roots, 

 through which pass the afferent fibres of the nerve of that muscle. Again, 

 under decerebrate rigidity, ankle-clonus is obtainable (cat) when all the 

 nerves of both hind limbs have been severed, excepting only the nerve of 



* Cf. ' Eoy. Soc. Proc.,' vol. 66, p. 66 ; and vol. 76, B, p. 291. 



t ' Zeitschrift f. Biologie,' vol. 44 ; ' Ergebnisse d. Physiologie,' 1904, p. I. 



| ' Eoy. Soc. Proc.,' vol. 52, p. 557. 



