486 Journal of Applied Microscopy. 



The normal nerve consists of primitive fibrils imbedded in a perifibrillar 

 matrix and enveloped in three sheaths, the sheath of Schwann, the medullary- 

 sheath, and an inner sheath. Monckeberg admits the possible granular structure 

 of the fibrils, but considers that the granules are more in the nature of molecules 

 and not visible. The fibrils are of the same thickness throughout and are free 

 from varicosities. The sheath of Schwann, the medullary sheath, and the peri- 

 fibrillar substance are broken into segments at the nodes of Ranvier, but the 

 fibrils are continuous from the centrum to the peripher}^ This is taken as evi- 

 dence that the primitive fibrils form the conducting substance. 



A delicate line may be seen between contiguous segments of the nerve, giving 

 the impression that the substance of the two segments is separated by a capillary 

 space, and a precipitate is formed here in material fixed with osmic acid, or 

 silver solution. 



The study .of the degenerating nerve showed that the fibril consists of two 

 parts, an insoluble substratum, and a substance in chemical or mechanical union 

 with this which is easily soluble in alkalies and reacts to basic stains. When 

 this stainable substance is gone the nerve loses its irritability. Degeneration 

 depends upon changes set up in the primitive fibrils, and going hand in hand with 

 changes in the matrix. The fibrils form spindle-shaped thickenings and break 

 up into coarse granules, which fragment and are resorbed. Degeneration begins 

 at the point of lesion, and is total toward the periphery, but partial toward the 

 centrum. The rate of degeneration varies in summer and winter frogs. Sen- 

 sory fibers degenerate more rapidly than motor fibers, degeneration is more rapid 

 in thin than in thick fibers, and it varies in different parts of the same fiber. 

 There does not appear to be sufficient proof of a difference between traumatic 

 and secondary degeneration. e. m. b. 



This is an investigation of the question 

 Abraham, Dr. Die Durchschneidung des Ner- which has been under discussion for the 

 vus Mandibularis. Archiv. f. Mikr. Anat. j^g^ f^^^y yg^rs as to the existence of 

 54: 224-254, pi. XII, wdth 8 text-figs., 1899. ■' ■' 



trophic nerve fibers. Experiments were 



made upon kittens, and upon about forty dogs ranging in age from eight days to 

 three or four months. The teeth were chosen for study, partly from the writer's 

 familiarity with that tissue, and partly because the tissue, being highly differenti- 

 ated, does not possess a variety of functions which would complicate the investi- 

 gation of a single series of changes that might be set up. The innervation of 

 certain teeth was destroyed by cutting the mandibular nerve of the left side, and to 

 prevent regeneration, as much of the nerve as could be reached — a half centimeter 

 at least — \vz.s extirpated. The right side was left intact for comparison. The 

 wounds healed readily, and later both left and right sides of the under jaw were 

 removed and placed in picric-acetic-sublimate, decalcified with three per cent, 

 nitric acid, imbedded in celloidin, and stained after the Van Gieson method. In 

 the forty cases there were no histological differences between the teeth of the 

 right and left sides except in one instance, where the slight changes presumably 

 resulted from injury to the artery supplying the tooth. A quantitative chemical 

 analysis of teeth from each side showed 20. (> per cent, of organic matter and 

 56.58 per cent, of lime in those from the right side and 19.3 per cent, organic 



