THE LAWS OF HABIT. 437 



It must be noticed that the growth of structural modification in 

 living matter may be more rapid than in any lifeless mass, because the 

 incessant nutritive renovation of which the living matter is the seat, 

 tends often to corroborate and fix the impressed modification, rather 

 than to counteract it by renewing the original constitution of the tis- 

 sue that has been impressed. Thus, we notice after exercising our 

 muscles or our brain in a new way, that we can do so no longer at 

 that time ; but after a day or two of rest, when we resume the disci- 

 pline, our increase in skill not seldom surprises us. This has led a 

 German author to say that we learn to swim during the winter and to 

 skate during the summer. 



Dr. Carpenter writes :* " It is a matter of universal experience, 

 that every kind of training for special aptitudes is both far more ef- 

 fective, and leaves a more permanent impress, when exerted on the 

 growing organism, than when brought to bear on the adult. The 

 effect of such training is shown in the tendency of the organ to 'grow 

 to ' the mode in which it is habitually exercised ; as is evidenced by 

 the increased size and power of particular sets of muscles, and the ex- 

 traordinary flexibility of joints, which are acquired by such as have 

 been early exercised in gymnastic performances. . . . There is no 

 part of the organism of man in which the reconstructive activity is so 

 great, during the whole period of life, as it is in the ganglionic sub- 

 stance of the brain. This is indicated by the enormous supply of blood 

 which it receives. ... It is, moreover, a fact of great significance 

 that the nerve-substance is specially distinguished by its reparative 

 power. For while injuries of other tissues (such as the muscular) 

 which are distinguished by the speciality of their structure and endow- 

 ments, are repaired by substance of a lower or less specialized type, 

 those of nerve-substance are repaired by a complete reproduction of 

 the normal tissue ; as is evidenced in the sensibility of the newly 

 forming skin which is closing over an open w r ound, or in the recovery 

 of the sensibility of a piece of "transplanted" skin, which has for a 

 time been rendered insensible by the complete interruption of the con- 

 tinuity of its nerves. The most remarkable example of this repro- 

 duction, however, is afforded by the results of M. Brown-Sequard's f 

 experiments upon the gradual restoration of the functional activity of 

 the spinal cord after its complete division ; which takes place in a way 

 that indicates rather a reproduction of the whole or the lower part of 

 the cord and of the nerves proceeding from it, than a mere reunion of 



Spencer there tries, not only to show how new actions may arise in nervous systems and 

 form new reflex arcs therein, but even how nervous tissue may actually be born by the 

 passage of new waves of isomeric transformation through an originally indifferent mass. 

 I can not help thinking that Mr. Spencer's data, under a great appearance of precision, 

 conceal lamentable vagueness and improbability, and even self-contradiction. 



* "Mental Physiology," 1874, pp. 339-345. 



f [See, later, Masius in Yan Beneden's and Van Bambeke's " Archives de Biologic," 

 vol. i, Liege, 1880.— W. J.] 



