[mills] functional DEVELOPMENT OF CEREBRAL CORTEX 5 



and with a distance between their extremities varying with the size of 

 the brain to be stimuhited — this distance never baing gi-eater than a few 

 millimetres — were used to convey the stimulus to the brain. 



It was found desirable to use about four different strengths of 

 current : (1) A current felt distinctly on the tongue, but easily tolerated ; 

 (2) a current readily felt on the lips, but tolerable ; (3) a current not to 

 be borne on the lips without inconvenience ; (-i) a cui'i-ent too strong to 

 be borne on the lips at all without positive pain. These will b^^ desig- 

 nated currents A. B. C. D, respectiveh'. 



Occasional!}" a current stronger still was employed, such as could not 

 be borne on the skin anj'where. This will be designated •• strongest 

 current,'" as it was the strongest to be obtained b}' the use of one 

 Daniell's cell or its equivalent. Such a current is generally useless, 

 howevei\ in brain work, on account of the readiness with which it passes 

 beyond the area of stimulation ; nevertheless, as will appear later, it has 

 sometimes served a good purpose. 



Difficulties. 



So delicate, ill-organized, un.stable are the motor centres of the very 

 young animal that it requires great care to get at the exact state of 

 atfairs and avoid fallacies. 



In my experience, haemorrhage is the greatest difficulty and source 

 of fallacy. Sometimes a very moderate loss of blood seems to suffice to 

 ruin the activity of a centre ; at other times the centre remains function- 

 ally active in spite of haemorrhage, exposure to the air, etc. 



In some cases a few stimulations seem to exliaust, if not to destroy, 

 the centre, even when very moderate currents are used. 



Xaturally, the younger the animal the greater the difficulties and the 

 more carefully the source of fallacy must be guarded. The longer I 

 continued my researches the more I became impi'essed with this, as well 

 as with tlie wide margin of individual difference in animals, and this 

 accounts in part for the large number of experiments I have been 

 obhged to make to satisf}' myself as to the correctness of my i-esults. 

 In not a few cases no positive conclusions could be drawn at all. 



EXPERIMENTAL RESULTS. 



I.— The Dog. 



A number of puppies, some of them pure-bred St. Bernards (bitches), 

 others cro.ss-bred, were tested when very young, vi^., from 36 hours up to 

 the 8th day. The result, no matter what strength of current was used, 

 was absolutely negative as regards both the cortex and the white matter 

 beneath, except in one case, to which I now refer in detail. 



