26 Foster, Physical Basis of Psychical Events, 



Moreover, when we come to inquire why, in the monkey 

 and in ourselves, injury to or disease of the occipital 

 cortex abolishes or interferes with visual sensations, we 

 have to bear in mind the following important facts. 

 Removal or disease of the occipital cortex in such cases 

 has effects which are not confined to the cortex; the lower 

 bodies, the corpus geniculatum, the pulvinar and, in part, 

 the corpus quadrigeminum are secondarily affected ; their 

 nutrition and life is interfered with, they undergo degene- 

 ration. The life of the nerve cell in the corpus genicu- 

 latum, whose axon stretches away to end in the occipital 

 cortex, is in some way dependent on the integrity of the 

 termination of that axon in the cortex; cut away that 

 termination and the whole unit suffers. In such cases the 

 removal of the cortex means more than mere absence of the 

 cortex, it means interference with the rest of the mechan- 

 ism. The absence of visual sensations in these circum- 

 stances cannot be attributed to mere absence of cortex ; it 

 may be in part due to changes in the lower part of the 

 mechanism — changes which early manifest themselves by 

 functional deficiencies, and later on by visible structural 

 alterations. Indeed, the difference between the effects of 

 removing the cortex in the monkey and those of the same 

 operation in the rabbit or bird may be simply an expres- 

 sion of the much closer dependence on each other of the 

 several parts of the mechanism in the one case than in the 

 other, the dependence being itself the outcome of a higher 

 psychical development. 



So close, indeed, is this dependence of the lower visual 

 body on the cortex, so delicate the ties which bind them 

 together, as to justify the doubt whether the nervous events 

 which take place in this part of the visual mechanism are 

 to be considered as of the same order as the more ordinary 

 nervous impulses known to us by our studies on ordinary 

 nerves. Some time back I gave a warning, that such an 



