154 E. A. Schäfer, 



Table III. 

 In this table T denotes excitation of the superior temporal gyrus, 

 and of the surface of the occipital lobe. 



T 



T 







T 







.2 



.2 



.2 



.15 



.15 



.15 



There is one possible source of error which I was unable entirely 

 to eliminate in these experiments ; that namely which might arise from 

 the anaesthetic employed acting more powerfully upon the posterior 

 than upon the anterior excitable regions. That it does so act is pro- 

 bable from the fact that with deep anaesthesia not only is the latency 

 of both regions increased but the difference between them is also in- 

 creased, not only absolutely but proportionally. Although this of itself 

 indicates a difference in their mode of action, nevertheless it would 

 be desirable to eliminate it by one or more experiments without anaes- 

 thetics. I have not actually done such, but I have on several occasions, 

 after the production of a deep anaesthesia, reduced the administration 

 of ether to a minimum, or have even desisted for some time from ad- 

 mistering a fresh supply. Under these circumstances the sleep induced 

 by the anaesthetic remains, if the monkey be undisturbed, and very 

 weak excitation of the cortex may produce the requisite movement 

 of the eyes without awakening the animal. In such cases the period 

 of latency for both frontal and posterior regions is considerably 

 shortened, but the difference between them is still well marked. It 

 would appear therefore, that there is a difference in the periods of 

 latency of the anterior (motor) and posterior (sensory) centres of some 

 hundredths of a second. This can mean nothing else than that there 

 is at least one other nerve centre interpolated between the excited 

 grey matter and the muscles which are called into action. And it 

 seemed to me at first sight most probable that this extra centre is 

 none other than the anterior (motor) centre itself, which might well 

 be supposed to be called into action by impulses proceeding along 

 intracentral tracts from the excited posterior cortex. That this is 

 not necessarily the case is shown however, by the following experiment : 



