94 TEXT-BOOK OF PHYSIOLOGY 



termination, however, nerve-fibers retain their individuality, and never be- 

 come blended with adjoining fibers. 



As nerves pass from their origin to their peripheral terminations, they 

 give off a number of branches, each of which becomes invested with a 

 lamellated sheath an offshoot from that investing the parent trunk. This 

 division of nerve-bundles and sheath continues throughout all the branchings 

 down to the ultimate nerve-fibers, each of which is surrounded by a sheath 

 of its own, consisting of a single layer of endothelial cells. This delicate 

 transparent membrane, the sheath of Henle, is separated from the nerve- 

 fiber by a considerable space, in which is contained lymph destined for the 

 nutrition of the fiber. Near their ultimate terminations the nerve-fibers 

 themselves undergo division, so that a single fiber may give origin to a num- 

 ber of branches, each of which contains a portion of the parent axis-cylinder 

 and myelin. 



FIG. 44. TRANSVERSE SECTION OF A NERVE (MEDIAN), ep. Epineurium. pe. Perineurium. 

 ed. Endoneurium. (Landois and Stirling.) 



Sympathetic Ganglia. A sympathetic ganglion consists essentially of 

 a connective-tissue capsule with an interior framework. The meshes of 

 this framework contain nerve-cells possessing dendrites and branching 

 axons. The majority of the axons are devoid of myelin and are therefore 

 known as non-myelinated nerve-fibers. Owing to the absence of the myelin 

 they present a rather pale or grayish appearance. In all instances, with 

 the exception of the ganglion cells of the heart, the axons are distributed to 

 non-striated muscle tissue and to the epithelium of glands. 



The nerve-cells of the ganglia are also in histologic connection with the 

 terminal branches of certain fine medullated nerve-fibers which leave the 

 spinal cord by way of the ventral roots of the spinal nerves. These nerve- 

 fibers are designated pre-ganglionic fibers, while those emerging from the cells 

 are designated post-ganglionic fibers. 



Blood-supply. Nerves being parts of living, cells require for the main- 

 tenance of their nutrition a certain amount of blood. This is furnished by 

 the blood-vessels ramifying in and supported by the connective-tissue frame- 

 work. Here as elsewhere there is a constant exchange, through the capillary 

 wall and the neurilemma, of nutritive material to the nerve proper and of 

 waste materials to the blood. 



The Chemic Composition and Metabolism. Chemic analysis of 

 nerve-tissue has shown the presence of water, proteins (two globulins, a 

 nucleo-protein and neurokeratin), certain lipoids, e.g., (a) cholesterin (a 

 monotomic alcohol free from both nitrogen and phosphorus), (b) several 



