48 THE NERVOUS SYSTEM 



and, because it contains little chromatin, it stains lightly with the basic dyes 

 (Fig. 27, A). It contains a large spheric nucleolus. The cytoplasm, enclosed 

 in a cell membrane, is characterized by the presence of basophil granules and 

 a fibrillar reticulum. The granules, which apparently are a product of the 

 nucleus, are composed of nucleoprotein. They are grouped in dense clumps, 

 known as Nissl bodies or tigroid masses, and stain deeply with methylene-blue. 

 The size, shape, and arrangement of the Nissl bodies differ with the type of 

 nerve-cell studied. They are much larger in motor than in sensory neurons 

 (Malone, 1913). While they are found in the larger dendrites, the axon and 

 its cone of origin are free from them. They are intimately concerned in the 



Axon 



Fig. 27. Nerve-cells stained with toluidin blue: A, From anterior horn of spinal cord of the 

 monkey, shows Nissl bodies in cytoplasm; B, from the facial nucleus of a dog, shows a partial 

 disappearance of the Nissl bodies (chromatolysis) resulting from section of the facial nerve. 

 (Schafer.) 



metabolic activity of the cell, increasing during rest and decreasing as a result 

 of fatigue. They also undergo solution as a result of injury to the axon even 

 at a great distance from the cell, the so-called axon-reaction or chromatolysis 

 (Fig. 27, B). 



The neurofibrils were first brought forcefully to the attention of neurologists 

 by Bethe (1903). These are delicate threads which run through the cytoplasm 

 in every direction and extend into the axon and dendrites (Fig. 28). The 

 appearance of the fibrillae differs according to the technic employed in preparing 

 the tissue for microscopic examination. While in the preparations by Bethe's 

 method the fibrils do not appear to branch or anastomose with each other, those 

 seen in Caial preparations divide, and by anastomosing with each other form 



