288 NEEVE-TISSUE. 



The reticular structure of these bodies was first described by 

 C. Frommann, in 1867. This reticulum is usually very distinct, 

 especially when the formations of nuclei, nucleoli, and nucleolini 

 (L. Mauthner) are well marked. The reticular structure is not 

 peculiar to these bodies, but is one of the general features of all 

 bioplasson. The offshoots of the ganglionic elements are of two 

 kinds : the broad, so-called protoplasmic offshoots of Deiters, and 

 the narrow, axis-cylinder offshoots. Of the former, we know that 

 they connect neighboring elements and branch out into the 

 gray substance, where they divide into an extremely delicate 

 reticulum, first described by T. Gerlach. This author further 

 asserts that the ganglionic elements of Clarke's columns, and 

 perhaps those of the posterior horns also, have no other than 

 branching offshoots. The narrow axis-cylinder offshoot takes 

 a more or less straight course, and enters the white substance 

 without ramifications, thus being a future nerve-fiber. Axis- 

 cylinder offshoots arise also from the gray substance, without 

 any connection with ganglionic elements. 



M. Schultze and others maintain that the axis-cylinder has a 

 delicate fibrillated structure, and that the fibrillae spread in the 

 body of the ganglionic element after the manner of a fan. This 

 assertion is based upon observation of teased specimens, and 

 should be cautiously received. I have often studied the brain 

 structure of freshly killed rabbits, both with and without the 

 addition of an indifferent liquid, and could never discover any 

 fibrillated structure in the axis-cylinders. Both the broad 

 axis-cylinders and the broad offshoots have a delicate reticular 

 structure, like that seen in the ganglionic elements themselves. 

 The finest axis-cylinders are apparently solid or slightly vacu- 

 oled. In the gray substance, especially in young animals, many 

 axis-cylinders exhibit varicose enlargements, which are consid- 

 ered by histologists to be post-mortem appearances. This, 

 again, is an, assertion which I must contradict, as I have fre- 

 quently observed such enlargements in fresh specimens (see page 

 129, Fig. 43). I must also contradict the assertion of histologists 

 that medullated nerve-fibers arise directly from ganglionic ele- 

 ments. These bodies are present only in the gray matter, where 

 no medullated nerve-fibers exist, but only bare axis-cylinders ; 

 obviously, therefore, the axis-cylinder, emanating from the gan- 

 glionic body, must run for a certain distance without a myeline 

 investment. 



Very little is known regarding the course taken by the nerve- 



