OPENING ADDKESS. 21 



lobes of the cerebral hemisphere. Histology, unaided, could 

 find no change in these cells in consequence of nerve 

 impulses having followed one another through this nervous 

 chain, but lately structural alterations in these cells have 

 been ascertained, the road for this discovery having been 

 made by the more accurate physiological knowledge of 

 cerebral function which physiological experiment has 

 revealed. If one eye of an animal be bandaged, the 

 animal exposed to light and then killed, on examining the 

 nerve cells in the retina, and in the particular regions of 

 the brain just referred to, it is seen that the cells on the 

 side of the bandaged eye are quite different in appearance 

 to those on the other side. 



Those through which the nervous impulses passed show 

 alterations both in the size of their nuclei and in the 

 micro-chemical characteristics of their protoplasm. This 

 research, hardly yet completed by Dr. Mann of Edinburgh, 

 is undoubtedly the initial step of a great histological 

 inquiry, and to this field physiology has guided the micro- 

 scopist ; function has thrown light upon structure.* 



That there is an inference in the above, is no doubt true, 

 and this is well illustrated by the last instance to which I 

 can allude to-night — one of the most brilliant of all the 

 discoveries connecting function and structure. 



The sense organs themselves, not merely the nerves and 

 nerve-cells, but the cellular apparatus which is acted upon 

 by the external force, which, in the case of the eye, 

 transmutes in its living crucible waves of light into visual 

 nerve impulses, this peripheral organ changes in structure 

 in consequence of the action upon it of the external agent. 



If the frog's eye be exposed to light, and the retina 

 contrasted as to structure with an eye kept in the dark, 



* Mann. Changes in Nerve Cells. Journal of Anatomy and Physiology, 

 Vol. XXIX, p. 100. 



