718 THE CEREBELLUM 



45 grams in individuals between the ages of 20-30 

 50 grams in individuals between the ages of 30-40 

 60 grams in individuals between the ages of 50-60 



The capacity of the ventricles is 26 c.c, and the specific gravity of 

 the entire encephalon 1.036. Its weight varies considerably even when 

 members of the same race and social standing are compared. Thus, 

 the compilations of Marshall^ which are based on the records of 

 Boyd, show immediately that the male possesses a heavier encephalon 

 than the female and that all its subdivisions are heavier. Further- 

 more, a comparison of individuals of the same sex and age will show 

 that those having the greater stature, exhibit a greater brain weight, 

 and that the weight decreases with advancing years. This decrease 

 in weight is most clearly indicated between the seventy-first and 

 ninetieth years. 



Vierordt^ has collected a series of observations illustrating the 

 changes in the weight of the brain between birth and the twenty-fifth 

 year; which show that the greatest increase takes place during the 

 first year. It grows rapidly to the fourth and fifth years, and then 

 more gradually to the seventh year. From this time on its growth is 

 very slight up to maturity. Social environment may be expected to 

 be of influence, because the least favored individuals in any community 

 usually show a certain retardation. The observations of Manouvrier 

 have proved, however, that the average weight of the brains of murder- 

 ers permits of no conclusions when compared with the average weight 

 of the brains of the usual inmates of hospitals. Moreover, with the 

 exception of, the microcephalics, the insane as a class are not 

 characterized by an especially slight brain weight. The examination 

 of the brain capacities of a series of skulls belonging to different 

 races, favors the western Europeans. ^ 



The total number of neurons present in the central nervous 

 system, has been estimated at 13,000,000,000. This estimate is 

 based upon the records of Hammarberg,^ which in accordance with 

 Thompson,^ give 9,200,000,000 well-marked cell-bodies to the cortex 

 of the cerebrum alone. 



The Cerebrospinal Fluid. ^ — The subarachnoidal and subdural 

 spaces, as well as the encephalic ventricles, are filled with a colorless 

 liquid, the quantity of which varies between 60 and 200 c.c. in accord- 

 ance with the age and size of the individual. The subdural space 

 being chiefly potential, about one-half of this quantity is held in the 

 subarachnoidal clefts, and 20-30 c.c. in the ventricles We have noted 



^ Jour, of Anat. and Physiol., 1892. 



2 Archiv fur Anat. u. Physiol., 1890. 



3 Davies, Jour, of the Acad, of Nat. Sciences, Philadelphia, 1869; also: Donald- 

 son, The Growth of the Brain, 1895. 



* Studien iiber die Path, der Idioten, Upsala, 1895. 



6 Jour, of Comp. Neurol., 1899. 



^ First described by Haller, Physiol, des Menschen, 1766. 



