498 MESSRS. F. GOTCH AND V. HORSLEY 



coming to the centre approaches it by way of the pyramidal tract which runs in the 

 lateral column, and is marked as a thick interrupted line in the diagram and by the 

 letters py. 



To obtain the time loss we have as before to take the total time expended from the 

 moment of excitation at L to that of the contraction of the muscle M, and then to 

 subtract from it the time occupied in simple transmission along the line L/M, and, 

 finally, to subtract the latency time of the muscle. These times are as follows : 



DELAY in the Spinal Centre during Excitation of the Lateral Column. 



Average of four 



experiments (Cats). 



Second. 



1. Total expenditure of time from L to M 'OJ76 



2. Time expended in transmission from L to f, and 



E to M '006 



3. Time expended in latency of muscle '01 



On subtracting 2 + 3 from 1, we get as a final result '0016. This resultant loss of 

 time is thus several thousandths of a second shorter than the delay taken by trans- 

 mission of the reflex effect. This is naturally to be expected as a consequence of the 

 lesser amount of centre to be traversed, but possibly the smaller result is also due 

 to the channel of the pyramidal path in the nerve centre being " polarised " for 

 descending and efferent impulses. 



It appears, therefore, that when the impulses have to pass through the whole 

 central structure (as in reflex) they suffer both a delay in time and a very marked 

 reduction in quantity, and that when they pass through a portion which excludes the 

 afferent commencement of the centre (cortical discharges), although the reduction is 

 very considerable, the delay is much less. 



There is one point to which it is necessary to draw attention before leaving this 

 part of the subject, namely, the well-known susceptibility of central mechanisms to 

 changes from fatigue, these altering the amount of nerve energy discharged. It will 

 be sufficient here to indicate by two examples the influence which previous activity has 

 upon the amount of nerve energy reflexly discharged from a spinal centre, the latter 

 being indicated by the electrical effect iu the issuing nerves. 



