270 F. W. (ARPENTER AND J. L. CONEL 



cells, chiefly those of Dogiel's type II. In some cases the centrip- 

 etal fibers of such neurones are believed to end within sympathetic 

 ganglia in connection with the dendrites of efferent cells. 



A considerable amount of indirect evidence in support of the 

 latter view has accumulated from various sources. It has been 

 repeatedly shown that during development the embryonic spinal 

 ganglia (which later, when functional, are entirely sensory) con- 

 tribute cells to the forming sympathetic ganglia. The experimen- 

 tal demonstration of reflexes in the domain of the sympathetic 

 system after communication with the spinal nerves and cord has 

 been severed seems to indicate the presence of entire local sensory 

 elements capable of acting as the afferent arm of a reflex arc. 

 However, it should be recalled that Langley explains such re- 

 actions by his ingenious "axon reflex " hypothesis, which takes into 

 account only neurones that are ordinarily efferent in character. 

 From anatomical sources comes such indirect evidence as that 

 furnished by the comprehensive study of the elements of spinal 

 ganglia made by Dogiel ('08). Non-medullated fibers terminat- 

 ing within spinal ganglia in the form of pericellular end-nets 

 have been assumed to come from the sympathetic system. That 

 is to say, they are regarded as the centrally directed processes 

 of afferent autonomic neurones, the cell-bodies of which lie in 

 sympathetic ganglia. 



With these facts pointing to the existence of intrinsic sensory 

 neurones, we might expect to find confirmatory evidence in the 

 direct histological examination of the tissues concerned. Can it 

 be shown under the microscope that sensory and motor neurones 

 with differential structural characters occur? In the cerebro- 

 spinal system of peripheral nerves such characters are, as is well 

 known, easily demonstrable. 



A perusal of the literature seems to indicate that practically 

 the only direct observations on what appear to be distinct sen- 

 sory and motor types of sympathetic cells are those recorded by 

 Dogiel ('96), for mammals and other vertebrates, in his article 

 entitled, ''Zwei Arten sympathischer Nervenzellen." A number 

 of authors (Cajal, Miiller, Michailow) have, it is true, described 

 different varieties of autonomic cells, Michailow recording no 



