278 AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



viduals usually examined in the Parisian hospitals. In the same manner, the 

 observations on the h rain-weight among the insane indicate, according to the 

 records of Boyd and others, that the insane as a class (the microcephalics 

 being excluded) are not characterized by a special brain-weight. When, 

 however, the insane are grouped according to the form of disease from which 

 they have suffered, it is evident that those in which the brain was congested 

 at death exhibit the higher weight, while those in which the pathological 

 processes caused destructive changes, exhibit a low weight. The differences 

 in these case- arc rather the results of disease than the cause of it. 



Brain-weights of Different Races. — Concerning the weights of the brain 

 in different races there are no extensive observations which have been made 

 directly on the brain itself. Davis, 1 however, has determined the cranial 

 capacities of a series of skulls belonging to different races, and the brain- 

 weights have been calculated from these. 2 This calculation gives the largest 

 brain-weights to the western Europeans, but for a proper interpretation of 

 the results there are needed at least the data concerning stature and age of 

 the cases studied, both of which are here lacking. 



Weight of the Spinal Cord. — Comparatively few observations are avail- 

 able for the spinal cord : Mies 3 found that in adults it weighed 24 to 33.3 

 grams, with an average weight of 26.27 grams ; this for the cord deprived of 

 the nerve-roots but covered by the pia. The variations due to sex and stat- 

 ure have not been determined. It seems probable, however, that the cord, 

 like the brain, will be found lighter in females and in short persons: Mies 

 states that its decrease in old age i> proportionately less than that of the brain. 



B. Growth-changes. 



The characters of the brain and cord thus far described have been those 

 found in the adult. Between birth and the natural end of life, however, 

 great changes take place, and, as it is necessary to consider the functions of 

 the central system at all times in its history, the importance of knowing the 

 direction in which the growth-changes are probably occurring is obvious. 



Growth of the Brain. — The weight of the brain from birth to the 

 twenty-fifth year is shown in Fig. 118. The curve is based on the 

 table of Vierordt. 4 



The curve beyond the twenty-fifth year is continued on the basis of the 

 observations by Bischoff, 8 and for comparison the curve representing the en- 

 cephalic weights of a series of eminent men, forty-five in number, is drawn 

 in a dotted line, the averages for decennial periods being alone dotted. 



These records exhibit the fact that at birth the weight of the brain is about 

 one-third of that which it will attain at maturity. The increase is very rapid 



1 Journal of the Academy of Natural Sciences, Philadelphia, 1*69. 



2 Donaldson: Growth of the Brain, 1895, p. 115. 



3 Neurologischea Centralblatt, L893. 



* Archivfur Anatomic »>"/ Physiologic, 1890. 

 Hirngewicht da Menschen, Bonn, 1^80. 



