76 VETERINARY PHYSIOLOGY 



(p. 107), and when this is done the muscles supplied remain 

 soft, flaccid, and motionless. Under normal conditions no 

 impulses pass from the cells. 



2. Conduction? — That the cells do not play an essential 

 part in conduction has been most clearly demonstrated by 

 experiments upon the common crab, where it is possible to 

 remove the nerve cell from the fibre with which it is 

 connected without injuring the fibre. For some time after 

 this is done the fibre continues to conduct. 



3. Nutrition of the Neuron. — The function of the cell 

 is to preside over the nutrition of the neuron. It appears 

 to have the power of accumulating a reserve of material 

 which, when the cells are fixed, appears as Nissl's granules, 

 for it has been found that after continued action these 

 granules diminish in amount. The nucleus, too, gives ofif 

 material for the nourishment of the neuron, and in conditions 

 of excessive activity it has been found shrunken and dis- 

 torted. 



If any part of the neuron is cut off from its connection 

 with the cell, it dies and degenerates, and later the cell may 

 also undergo changes. 



(a) Degeneration and Regeneration of Nerves. — In the cat, 

 excitabihty disappears after three days (p. 60), and the white 

 sheath shows degenerative changes in eight days. The fatty 

 matter runs into globules and stains black with osmic acid, even 

 after treatment with chrome salts (Marchi's method). This 

 seems to be due to the fact that osmic acid acts upon the 

 unsaturated oleic acid, and that this, in the normal nerve, 

 is oxidised by the chrome salt, whereas, in the degenerated 

 nerve, so much is set free that it cannot all be oxidised, 

 and therefore stains with osmic acid. The white sub- 

 stance gradually disappears ; at the end of a month the 

 phosphorus has all gone, and by the end of about forty-four 

 days the fat can no longer be detected. At this stage 

 xMarchi's method is useless, and the degenerated fibres may 

 be demonstrated by the fact that they do not stain with 

 osmic acid or with Weigert's hrematoxyhn method which 

 stains the white sheaths of normal fibres. As the degenera- 

 tion advances, the axis cylinder breaks down, and the nerve 



