G20 NERVOUS SYSTEM. 



that the angle is larger in man than in any of the inferior animals and is 

 largest in those races that possess the greatest intellectual development. 



Pathological Observations. It is a fact now generally admitted in pathol- 

 ogy, that loss of cerebral substance from repeated haemorrhage is sooner or 

 later followed by impairment of the intellectual faculties. This point is 

 frequently difficult to determine in an individual instance, but an analysis of 

 a sufficient number of cases shows impaired memory, tardy, inaccurate and 

 feeble connection of ideas, abnormal irritability of temper with a childish 

 susceptibility to petty or imaginary annoyances, easily excited emotional 

 manifestations and a variety of phenomena denoting abnormally feeble intel- 

 lectual power, following any considerable disorganization of cerebral sub- 

 stance. In short, pathological conditions of the brain all go to show that 

 the intellectual faculties are directly connected with the cerebral hemispheres. 



In idiots the brain usually is of small size, although there are exceptions 

 to this rule. In two cases of adult idiots, reported by Tiedemann, the brain 

 was about one-half of the normal weight. The brain of an idiotic woman, 

 forty-two years of age, reported by Gore, weighed ten ounces and five grains 

 (about 284 grammes). It has been observed, also, that the cerebellum is 

 not proportionally diminished in size in idiots (Bradley). In one instance 

 reported, the proportion of the cerebellum to the cerebrum was as 1 to 5*5. 

 In the healthy adult male of ordinary weight, the proportion is as 1 to 8^. 

 The statements just made with regard to the brains of idiots refer to cases 

 characterized by complete absence of intelligence, and farthermore, probably, 

 by very small development of the body. On the other hand, there are 

 instances of idiocy, the body being of ordinary size, in which the weight of 

 the encephalon is little if any below the average. Lelut has reported several 

 cases of this kind. In one of these, a deaf-mute idiot, forty-three years of 

 age, a little above the ordinary stature, presenting "idiocy of the lowest 

 degree ; almost no sign of intelligence ; no care of cleanliness," the encepha- 

 lon weighed 48'32 oz. (1,369-8 grammes). Other cases of idiots of medium 

 stature are given, in which the brain weighed but little less than the normal 

 average. In the West Riding Lunatic Asylum Reports, London, 1876, is 

 a report of the case of a congenital imbecile, aged thirty years, height five 

 feet and eight inches (172-7 centimetres), died of phthisis, whose brain 

 weighed 70J- oz. (2,000 grammes). This is heavier than the heaviest normal 

 brain on record. The normal brain- weight is 49 oz. (1,408*3 grammes). 



Reaction-Time. The time which elapses between the application of a 

 stimulus and its appreciation by the individual experimented upon is known 

 as reaction-time. In experiments with reference to this point, the person 

 observed makes an electric signal when the sensation is perceived. The reac- 

 tion-time is 0-12 of a second for a shock on the hand, 0-13 for the forehead, 

 0-17 for the toe and 0-13 for a sudden noise (Exner). The duration is about 

 0-16 of a second for impressions made on the nerves of special sense. This is 

 the time of conduction of the impression to the brain, its appreciation by the 

 individual, the generation of the voluntary impulse and the conduction of 

 this impulse to the muscles concerned in making the signal. It is probably 



