March 27, 1885.] 



SCIENCE 



259 



are directed to tracing the course of the tracts 

 which unite the gray masses, and form the 

 parts of the projection system. Owing to the 

 discovery of new methods of investigation, 

 progress has been rapid of late. It is not to 

 be wondered at, therefore, that in regard to 

 some details, the statements of Meynert, which 

 were already in print three years ago, cannot 

 now be accepted ; e.g., as to the course of the 

 lemniscus (pp. 94-97), and the connection of 

 the tracts in the spinal cord with those in the 

 cerebral axis (pp. 120-125). The diagram 

 (fig. 58) is especially misleading. It is proba- 

 bly on account of these errors that an appendix 

 is promised, to appear with the second volume, 

 and to contain a review of the more recent dis- 

 coveries. These minor defects do not, however, 

 impair the usefulness of the work as a general 

 text-book of brain-anatomy ; and it is a matter 

 of congratulation to those who are unable to 

 master the very difficult st} T le of the author, 

 that an English translation is soon to appear. 



It is b}' means of the projection system that 

 impulses from without reach the brain-cortex, 

 and become conscious perceptions. To asso- 

 ciate these perceptions, and make connected 

 thought possible, there exists a second system 

 of fibres which unites the various regions of 

 the brain-surface with each other. This is the 

 4 association system.' Meynert illustrates the 

 action of these systems by analyzing the sim- 

 ple act of winking. If a pin touches the eye 

 of an infant, the lid closes. This is a reflex 

 act, carried out by a simple mechanism inde- 

 pendent of an} T act of consciousness ; but, 

 coincident with the reflex act, a number of im- 

 pulses are sent along the projection fibres to 

 the brain, which, on reaching the cortex, give 

 rise to the conscious perception of the appear- 

 ance of the pin, of the pain of the prick, and of 

 the motion which has been performed. Each 

 of these perceptions occurs in a different part of 

 the brain, since each impulse reaches it by a 

 different fibre. But the three occur simulta- 

 neously ; and, as all parts of the cortex are 

 joined b}' association fibres, the three percep- 

 tions are associated both in perception and in 

 memory. Hence, when the pin is seen again, 

 the memor}* of the pain arises, and also the mem- 

 ory of the motion which stopped the pain, and 

 thus the mere sight of the object may lead the 

 child to close the eye. The perception of the 

 reflex motion has given the infant the knowl- 

 edge of the possession of a muscle which will 

 move ; and the motion, having once become 

 conscious, can be reproduced voluntarily by an 

 effort which excites to action those cells which 

 retain the memory of the motion (pp. 144-148) . 



Every perception and motion has its appropri- 

 ate cell ; and, lest this should seem to demand 

 too great a number of cells, Meynert has exam- 

 ined the cortex microscopically, and has found 

 that it contains over a milliard of these bodies 

 (p. 140). Each physiological action is at- 

 tended by the acquisition of a new memory, 

 and, as we go on in life, the number of cells un- 

 occupied becomes less and less ; so that it is 

 probable that a plrysical limit to the power of 

 memory, and consequently to the power of in- 

 tellectual growth, is determined b}' the number 

 of cells in the cortex (p. 140) . This is the 

 stand-point of an extreme materialist. But 

 Meynert' s materialism is not of the theoretical 

 kind : it is based upon facts of observation which 

 cannot be ignored. The structure of the brain, 

 its comparative development in various species, 

 the evolution of mind in animals, the growth of 

 knowledge in children, the results of experi- 

 mental physiology, and the symptoms of men- 

 tal dissolution in a class of cases in which 

 disease has reduced the individual to the level 

 of the infant, or even to that of the brute, have 

 been called on to furnish the data for Mey- 

 nert's mechanism of thought. Psychologists 

 are slowly coming to the conclusion that a 

 wholly subjective method of research is inade- 

 quate to settle the questions which for so many 

 years they have been unable to answer, and 

 are beginning to pursue an objective method 

 by studying the development of mind, and the 

 disorders of mind which are associated with 

 actual loss of brain-substance. To psycholo- 

 gists, therefore, this book is of great impor- 

 tance ; for it opens up many new subjects, it 

 throws light on many obscure subjects, it set- 

 tles finally some disputed subjects. 



Physiological processes are attended by the 

 consumption of material : hence the nutrition 

 of the brain enters as a factor in mental action. 

 When a part of the brain is exercised, more 

 blood passes to that part than to other parts 

 to supply oxygen as it is needed. The rapidity 

 and quality of the mental process is dependent 

 to some degree upon the proper blood-supply. 

 These are facts determined by experiment on 

 animals and man. Mental labor is attended 

 with a rise of temperature in the brain, an in- 

 dication of increased oxidation processes. If 

 a dog's brain is laid bare, the vessels are seen 

 to be less distended with blood during sleep 

 than when it is awake. If the dog dreams, 

 the vessels dilate. An abnormal flow of blood 

 to the brain interferes with the natural action 

 of the organ : it ma}' cause an irritation of 

 the cells containing memory pictures, and con- 

 sequently a conscious perception of the object 



