J 27, 18S5.]
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��are directed to tracing the course of the tracts which unite the gray masses, and form the parts or the projection system. Owing to the discovery of new methods of investigation, progress has treen rapid of late. It is not to be woudered at, therefore, that iii regard to aoin« details, the statemeuta of Slejnert, which were already io print three years ago, eanuot now be accepted ; e.g., as to the course of the bmaiscus (pp. 94-97), and the connection of (he tracts in the spinal cord with thate in the cerebral asis (pp. 120-125). The diagram (fig. 58) is especially misleading. It ia proba- bly on accounlof these errors that an appendix Is promised, to appear with the second volume, Ekml to contain a review of the more recent dis- coveries. These minor defects do not. however, impair the nsefulneas of the work as a general t«xt-book of brain-anatomy ; and it is a matter of congratulation to those who are unable to zoaster the very difficult style of the author- that an English translation is soon Co appear.
It is by 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 '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, ibe lid closes. This is a reflex act, carried out by a simple niedianism inde- pendent of any 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 ap|iear- ftucc of the pin. of the pain of the prick, and of the motion which has been performed. Kach of these perceptions occurs in a different part of the brain, since each impulse reaches it by a different libre. But the three occur simulta- neously ; and. as all parts of the cortex are joined by association fibres, the three percep- tions are associated both in perception and in memory. Hence, when the pin is seen again, tbe memory 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 physiolopcal action is at- tended by the ac(|uisitiou of a new memory, ami. as we go on in life, the number of cells un- occupied becomes less and less; so that it is probable that a physical limit to the power of memory, and consequently to the power of in- tellectual growth, is determined by 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 isbased upon facts of observation which cannot be ignored. The structure of the brain, it« comparative development in various species. the evolution of mind in animab. 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 Bley- nert's mechanism of thought. Psychologists are slowly coming to the (.x>nclusion 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 arc 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. Tbe 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 o dog's brain is laid bare, the vessels are seen to be less distended with hlooii 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 may cause an irritation of the cells containing memory pictures, and con- Be<iuently a conscious perception of the object
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