136 



Mr. Graham Brown. 



be looked upon as produced by the " complete " relaxation of a proportion 

 of the muscle fibres — or by the " complete " inhibition of a proportion of the 

 efferent neurones. But Sherrington* has shown that the refractory phase 

 extends over the whole centre — just as Zwaardemakerf showed the same 

 phenomenon for deglutition. As regards this, the centre is therefore a unit, 

 and in some manner innervated as a whole from each afferent neurone. It 

 is, however, impossible to suppose that each afferent comes into direct 

 contact with each efferent in the mechanism.; and under any other supposi- 

 tion it is extremely difficult to realise the meaning of this unity if the 

 efferent discharges have an " all or none " character. 



IV. Methods here Employed. 



If a skeletal muscle exhibits a larger number of degrees of contraction 

 than there are efferent nerve fibres running to it, there must be a very 

 strong supposition that the reflex response has not an " all or none " 

 character. In such a case the deduction from the result would not need to 

 be influenced by the number of afferent fibres stimulated. 



Unfortunately, the large number of efferent fibres which supply most of 

 the skeletal muscles makes this experiment in their cases impossible. 



In the cat, however, a most beautiful muscle in the hind limb — tenuissimus 

 — seems almost to have been made for this experiment. 



This muscle is a thin band of only 2 or 3 mm. in breadth, but many 

 centimetres long. It arises from the caudal vertebrae at the root of the tail, 

 and passes down deep in the thigh, until it ends in the leg by blending with 

 the insertion of biceps. Tor the upper part of its length it lies near the 

 great sciatic nerve, from which, near its middle, it receives its nerve supply. 

 Occasionally it receives more than one nerve twig, and, in any case, its chief 

 nerve divides into two branches (occasionally into more than two) before 

 it reaches the muscle. The number of nerve fibres in each of these branches 

 is small. 



The cats used were decerebrate and low spinal. All the muscles of the 

 left hind limb were destroyed by motor paralysis. In the right hind limb 

 all were destroyed save tenuissimus. The great sciatic nerve was ligatured 

 after it had divided into external and internal popliteals. The biceps muscle 

 was divided transversely to its length about the middle, and tenuissimus 

 was thus exposed. 



All but the uppermost of the branches of its motor nerve were severed, 



* ' Journ. Physiol.,' vol. 31, ' Physiol. Soc. Proc.,' March 19, 1904 ; ' Journ. Physiol.,' 

 1906 ; vol. 34, p. 1. 



t ' Archives Internat. de Physiol.,' 1904, vol. 1, p. 1. 



