590 NERVOUS SYSTEM 



(Bradley). In one instance reported, the proportion of the cerebellum 

 to the cerebrum was as I to 5.5. In the healthy adult male of ordinary 

 weight, the proportion is as I to 8^. The statements just made in 

 regard to the brains of idiots refer to cases characterized by complete 

 absence of intelligence, and furthermore, probably, by very small de- 

 velopment 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 cleanli- 

 ness," the encephalon weighed 48.32 ounces (1369.8 grams). 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 cen- 

 timeters), died of phthisis, whose brain weighed 70^ ounces (2000 

 grams). This is heavier than the heaviest normal brain on record. 

 The normal brain-weight is 49^ ounces (1408.3 grams). 



Reaction-time. The time that elapses between the application of 

 sensory stimulus and its appreciation by the sensorium 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 

 reaction-time is 0.12 of a second for a shock on the hand, 0.13 for the 

 forehead, o. 1 7 for the toe and o. 1 3 for a sudden noise (Exner). The dura- 

 tion 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 probably is subject to variations analogous to 

 those observed in the " personal equation." 



Centre for the Expression of Ideas in Language. The location of 

 this centre depends entirely on the study of cases of disease in the 

 human subject. It is evident that there must be a comprehension of 

 the significance of words, the formation of an idea more or less complex 

 and a coordinate action of the muscles concerned in speech as condi- 

 tions essential to expression in spoken language. One or more of these 

 conditions may be absent in cases of disease ; and the general absence 

 of the power of verbal expression, when this depends on cerebral lesion, 

 is known as aphasia. This is quite different from aphonia, which is 

 simply loss of voice. If the comprehension of the meaning of words 

 is absent, the individual is incapable of receiving ideas expressed in 



