THE ORIGIN AND GROWTH OF BRAIN CELLS IN 

 THE ADULT BODY. 



By Howard Ayers. 



No part of our anatomical knowledge has had such slow 

 growth as that pertaining to the origin and growth of brain cells 

 and their ultimate relations to one another and to the rest of the 

 body. 



The current theory holds that after the nerve cell once 

 sends out its axis cylinder fiber and becomes a functional cell it 

 is incapable of division or further reproduction. For example 

 in the case of the human embryo it is stated that beginning 

 with the fourth week the neuroblasts continue rapid growth up 

 to the third month of fcetal life after which time no increase in 

 numbers takes place. All increase in the brain or its parts 

 after this period is due to the increase in size of the nerve cells 

 (from one to 500 times their original size), the increase in the 

 length and size of the sheaths of Schwann and the medullary 

 matter, the growth of the blood vessels and the neuroglia ele- 

 ments and the connective tissue additions to the brain. 



Double Auditory afid Electric Ganglion Cells. 

 In a former publication^ I figured and described some of 

 the cells of the cochlear ganglion as multipolar and in some cases 

 even as double cells. These latter cells were found to be com- 

 posed of two nucleated cell bodies closely connected by a short 

 connecting bar of protoplasm, in appearance like the peripheral 

 and central fibers given off from the other ends of these two cells 

 {cf. loc. cit., PI. I, fig. 6, x). The origin of these double cells 

 I was unable to trace at that time but their occurrence in the 

 ganglion was of interest to me in connection with the explana- 

 tion of the origin and relations of the hair cells. In my recent 



'The Auditory or Hair Cells of the Ear and their Relations to the Auditory 

 Nerve, Journ. Morph., Vol. VIII, No. 3, 1893. 



