MENTAL FUNCTION 421 



If there is a speech-center, then, in the brain, it is not because the in- 

 tellectual processes involve only this small area of the brain, but because 

 some directing knot of neurones is necessary here as elsewhere. Appar- 

 ently all the centers, nerve-paths, and muscles concerned in speaking, 

 writing, drawing, or otherwise representing ideas as concepts constitute 

 the special physical basis of cognition. (See the discussion of speech in 

 the latter part of the chapter on the Muscles, page 394.) 



Jennings' work on the mental process of infusoria is of fundamental 

 value in the theory of the relation of body and mind. 



MEMORY is the faculty by which organisms retain their experiences. 

 As we have already noted, it is the basis on which habits are formed, and 

 in general terms mental and bodily processes are inconceivable without 

 it. Corresponding with memory must be traces of some sort in the 

 body-protoplasm, but of the nature of these records no one as yet has 

 the slightest notion. We know only certain of the laws which appear to 

 underlie the function in the organism. 



Almost more than any other attribute of mind, memory is a natural 

 gift, and it varies greatly in its perfection in different individuals. A good 

 memory is a true gift of fortune for it ordinarily does as much as any 

 other thing to bring success in life, since he who has it possesses a double 

 and quadruple store of percepts and of concepts at his instant command. 

 This is the more important because it appears that the memory is little 

 capable of true development. One may acquire the habit of trying to 

 remember and thus practically enlarge to some extent his memorizing 

 powers, but observation no less than actual experiment in the laboratories 

 shows that the grasp and range of this recording and recalling faculty 

 can be little developed by any known means. We have to look espe- 

 cially in the nervous system for the innate difference in memories, 

 and it may be surmised to have its basis in some unknown plasticity 

 and tenacity of protoplasm especially of the neural variety: "wax to 

 receive and marble to retain." 



Sleep is another condition quite as evidently physiological as psycho- 

 logical. From either view-point there are many things about it still 

 unknown and the subject therefore of dispute. Still, much that is 

 definite about its psychophysiology is fairly well settled. In ancient 

 times the mystery of sleep found expression in some of the most striking 

 .suppositions and superstitions of all anthropology. 



The reason for sleep lies obviously in the fact that all finite, material 

 things wear out, and to continue acting require renewal. Entirely de- 

 prived of sleep a person would live only about a week perhaps not so 

 long. A few organs which work intermittently, for example the heart, 

 rest amply between actions, but the majority work continuously, as it 

 were, for longer periods and demand corresponding periods of rest in 

 order that the wear and tear may be repaired and that anabolism may 

 restock the tissue with efficient energies. For this repair in the muscles 

 or in the glands sleep is not required, for these refit themselves for work 

 by simple cessation of activity. It is the neural tissues apparently that 



