TRANSACTIONS OF THE SECTIONS. 137 



ultimate particles witliiti certain limits of movemeut. It alstj </i\c3 penetrability 

 by liquid diffusion, -while excluding- porosity and its capillary ellects, by -vvliich 

 means a ready nutrition by diffusion in one direction, and ready cleansing from the 

 effete crystaUizable products of life in another are assured. Consequently the brain 

 as a -whole is essentially made up of colloid matter, and may be compared to a 

 colloid septum, on the one side of -which is arterial hood and cerebro-spinal fluid of 

 the \ entricles ; on the other side, lio-weAer, is cerebro-spinal fluid of the arachnoideal 

 space and venous blood. It follo-ws from this that the large amount of -water pre- 

 sent in the brain is not there, so to say, mechanicallj' only, like water in a sponge, 

 and capable of being pressed out mechanically, but is chemically combined as colloid 

 hydration Avater, or, better, -v\-ater of coUoidation." 



Dr. Thudicum divides a large amount of the matter occurring in the brain into 

 three groups, viz. phosphorized bodies, consisting of carbon, oxygen, hydrogen, 

 nitrogen, and rich in phosphorus; nitrogenized bodies', containing only carbon, 

 oxygen, hydrogen, nitrogen, and no phosphorus ; and, third, oxygenized bodies, 

 formed of carbon, hydrogen, and oxygen alone. The phosphorized bodies he 

 divides into three subgroups, termed kephalines, myelines, and lecithiues. Each 

 of these has certain definite chemical characteristics, -which he summarizes as 

 follo-«-s : — " The kephalines possess the tendency to be oxydized, oxj^dizability ; the 

 myelines are not easily changed by any agent or influence, and possess therefore 

 stability ; the lecithines easily fall to pieces, they are afflicted with lability." 



lie then points out the remarkable tendency of the phosphorized bodies to com- 

 bine with other substances, showing a diversity of affinities " not possessed by any 

 other class of chemical compounds in nature at present known." He shows th.at 

 these affinities are influenced by the amount of water present, and by the mass of 

 the substance or reagent presented to the bram-matter, so that the interchange " of 

 affinities may produce a perfectly incalculable number of states of the phosphorized, 

 and consequently of brain-matter. This power of answering to any qualitative and 

 quantitative chemical influence by reciprocal quality or quantity we may term the 

 state of hibt'/c equilibrium ; it foreshadows on the chemical outside the remarkable 

 properties which nerve-matter exhibits in regard of its vital functions." 



jVll of these remarks by Ur. Thudicum point to a field of research which will not 

 be explored for many a year to come. But there can be little doubt that when the 

 chemical statics of the brain have been accurately ascertained, we will be in a 

 position to studv the chemical interchanges between the blood and the nervous 

 tissue. Should the skill of our physiological chemists succeed in unravelling these, 

 then we will be in a position to understand at least two different sets of phenomena. 

 These are— (1) the chemical changes which imdoubtedly take place during the 

 occurrence of mental phenomena ; and (2) the exact nature of the action of such 

 substances as alcohol, narcotics, and the various alkaloids which are kno-wu to act 

 on the nervous system. I need scarcely add that accurate knowledge regarding 

 the physiological action of these substances woidd probably be of great service in 

 the treatment of disease. 



Researchks on Sensohy iMpnr.ssiONs. 



In the second place, researches into the physiology of the senses afford another 

 series of data for the physiologist. These researches may be said to be of three 

 kinds — (1) inquiries into the anatomical and physiological mechanism of the sense- 

 organ itself, such as, in the case of vision, the general structure of the eye 

 as an optical instrument, and its movements by the action of muscles, so 

 as to secure the conditions of monocular or binocular vision; (2) inquiries 

 into the nature of the specific action of the external stimulus upon the 

 terminal organ of sense, and the transmission of tlie efi'ect to the brain — as, for 

 example, the action of light on the retina, and transmission along the optic 

 nerve ; and (3) experiments in which various stinudi are permitted to act imder 

 certain conditions on the terminal apparatus, and the result is observed and recorded 

 by the consciousness of the experimentaMst himself, as in researches on colour, 

 duration of impi-essions on the retina, positive and negative, after images, &c. By 

 these three modes of inquiiy a large number of facts relating chiefly to the senses 



