A NOTE ON THE SIGNIFICANCE OF THE SMALL 

 VOLUME OF THE NERVE CELL BODIES IN THE 

 CEREBRAL CORTEX IN MAN. 



By Henky H. Donaldson. 



Summary. 



(i) The weight of all the nerve cell bodies in the human 

 encephalon is less than 27 grams. 



(2) When comparison is made of human encephala 

 grouped according to race, sex, mental power, stature and age, 

 the differences in weight, within each group, are always more 

 than twice that of the nerve cell bodies, and hence these differ- 

 ences depend mainly on variations in the medullary substance. 



(3) Small variations in the mass of the nerve cell bodies 

 (though physiologically highly important) escape detection by 

 the method of weighing, or may be masked by the greater 

 growth of the medullary substance. 



The observations of Hammarberg' have been utilized by 

 Miss Thompson" to show that there are about 9,200,000,000 

 (nine-thousand two hundred million) nerve cell bodies in the 

 human cerebral cortex, and that they occupy but 1.37% of the 

 volume of the cortex. Concerning the essential correctness of 

 this unexpected result, there can be no doubt. It wiM be urged 



1 Studien Uber Klinik und Pathologic der Idiotic ncbst Untersuchungcn 

 liber die Normale Anatomie der Hirnrinde. Karl Hammarbcrg, Upsala, 1895. 



' The total number of functional nerve cells in the cerebral cortex of man 

 and of the percentage of the total volume of the cortex composed of nerve cell 

 bodies calculated from Karl Hammarberg's data ; together with a comparison 

 of the number of giant cells with the number of pyramidal fibers. (Journ. 

 of Comp. Neurol. Vol. IX, No. 3, 1899, pp. ii3-i4o-) 



