The Internal Senses. . 687 



certain of the cerebral arteries, the increased supply of blood in those 

 arteries, and ( as it appears ) the immediate differentiation of old cells, 

 and the formation of new ones. 



The cortical cells of the new-born infant are there by inheritance from 

 their parents. They are precisely in the physiological condition of the 

 buds on a maple, or other deciduous tree, in the spring. Those maple 

 buds are formed in the fall, and remain undeveloped till the flow of sap 

 up the tree in spring supplies the nutrient matter, and the warm sun- 

 light furnishes the force necessary to cause its assimilation by the em- 

 bryo leaf. So the infantile cerebral cell is a bud cell, and remains in 

 an inchoate state until an appropriate nerve current, formed by the trans- 

 mutation of sunlight, or some other form of energy reflected from some 

 external object, stimulates it, and directs to it a supply of the nutrient 

 blood. This action differentiates the cell, and forms it into a functional 

 or active organ, so that whenever i^; is stimulated in the future, its re- 

 action gives the sensation in memory of the object by which it was first 

 differentiated. As the child grows, there is a vast increase in the num- 

 ber of his cortical cells. These new cells are probably formed from the 

 old ones by budding, in a manner analogous to the budding of cells of 

 the saccharomyces cerevisiae (chap. 27), except that probably the process 

 is usually much more rapid, the only condition being the presence of 

 a superabundance of a healthy nutrient, and the stimulation of a ner- 

 vous current. Supposing a patch of cells to have become differentiated 

 by the sight of some particular object, say Minnehaha Falls. The next 

 time we see the Falls, I suppose the new sight stimulus is directed to 

 the same patch again, wherever that is, because the fact that it went 

 there first shows that towards it is the route of least resistance, for that 

 particular sort of stimulus. It is, without doubt, the hereditary route 

 which it takes, as the patch of cells to which it goes is the hereditary 

 patch for that sort of general stimuli, sight, sound, or whatever it may 

 be. Upon reaching its destination, those cells which the identical stim- 

 ulus differentiated before, are now only restimulated, and give a sensa- 

 tion of the memory of the place as we saw it before. But as it is im- 

 possible to see it twice precisely alike, there are now new elements of 

 stimulation which must cause the differentiation of fresh cells, if there 

 be any, or the budding of new ones from the old. So that every time 

 we see the Falls, the idea we get of them is a combination of former or 

 memory sensations, with new direct sensations. As there may be indefi- 

 nite repetitions of such process, an organ gets to be like a composite 

 photograph, which is made by superposing a dozen pictures upon the 

 same plate. The reflection from the organ is a composite reflection. 



The most obvious difference we discover between reflex actions of the 

 spinal cord and purposive actions, is that the latter are due to more 



