150 SCIENCE PROGRESS 



organ that was not even bilateral, for Willis there were two 

 souls, each widely diffused, the one in the blood, the other in 

 the nervous system. Willis asserted that the soul in the blood 

 was of the nature of a flame, that in the nervous system of 

 the nature of light. Willis's explanation of the way the soul 

 (through its derived spirits) was related to the brain was some- 

 what as follows : " The lighter and more spirituous parts of 

 the blood ascend by the arteries to the brain, where a distilla- 

 tion takes place, and animal spirits are the result. These 

 spirits flow over the surface of the cerebrum and cerebellum, 

 whence they descend all over the nervous system. Only the 

 spirits in the cerebrum are destined for voluntary movement 

 and sensation, those in the cerebellum are for involuntary 

 movement." This last idea is interesting in the light of 

 modern work, for although we cannot admit that, as stated, 

 it represents the truth, still it is a fact that the activities of 

 the cerebellum are carried on entirely outside the sphere of 

 consciousness. Undoubtedly Willis had glimmerings that 

 sensations and their memories — mental images — were on their 

 physical aspect modifications of the substance of the brain. 

 He talks of " the pictures or images of all sensible things 

 admitted into these secret places." One of Willis's books is 

 actually named De Anima Brutorum (concerning the soul of 

 animals). The soul, then, was by Willis allowed to reside in 

 the cerebral hemispheres, where it has ever since been permitted 

 to rest in peace, at any rate on the part of those who believe 

 that it needs a circumscribed dwelling within the bodily frame. 



When we come to the brilliant young man of science, the 

 Dane Nicholas Stensen (1638-1686), we come to the first attempt 

 to express the modern notion of localisation of function within 

 the brain, a truth parodied by the phrenologists, believed in by 

 the physiologists. This was how Stensen put it when writing 

 of the fibres in the white core of nervous matter : " If, indeed, 

 the white substance be wholly fibrous in nature, we must neces- 

 sarily admit that the arrangement of its fibres is made according 

 to some definite pattern, on which doubtless depends the 

 diversity of sensations and movements. It is my opinion that 

 the true method of dissection would be to trace the nervous 

 filaments to the substance of the brain to see which way they 

 pass and where they end ; but this method is accompanied with 

 so many difficulties that I know not whether we may hope ever 



