CIT. XIV.] CHEMISTRY OF NERVE DEGENERATION 167 



which is turned black on the addition of ammonium sulphide. His principal 

 results are : potassium is found in cell protoplasm, but more abundantly in inter- 

 cellular material ; in striped muscle it is limited to the dark bands, and in 

 pancreatic cells to the granular zone. It is not discoverable in any nuclei, nor in 

 nerve-cells, but in nerve-fibres is found in patches external to the axis cylinder. 

 Macdonald points out that these are spots which have been injured, and it is 

 apparently only on injury that the potassium is liberated in a form which renders it 

 detectable by Macalhim's reagent. 



Chemical changes in nervous tissues during activity. This is 

 an almost; unknown field. No change of reaction can be detected 

 in nerves after the most prolonged stimulation. The only thing known 

 for certain is that oxygen is essential, especially for the activity of 

 grey matter ; cerebral anaemia is rapidly followed by loss of conscious- 

 ness and death. The slight respiratory changes which can be detected 

 in peripheral nerves have already been considered on p. 158. It 

 can hardly be doubted that the phosphatides, which are extremely 

 labile substances, participate in metabolism ; and Hans Meyer has 

 pointed out that anaesthetics such as chloroform and ether are 

 soluble in lipoids, and that this interaction may by lessening 

 oxidative processes lead to the production of unconsciousness. 



Chemical changes in degenerative conditions. In Wallerian 

 degeneration of nerve, several investigators have attempted to dis- 

 cover how the degenerated nerve differs from a healthy nerve. 

 Little or no change in the peripheral end can be detected up to 

 about three days after a nerve has been divided, and the nerve-fibres 

 remain excitable up to that time. They then show a progressive 

 increase in the quantity of water, and a corresponding decrease in the 

 proportion of solids. The percentage of phosphorus also decreases, 

 and it entirely disappears in a little more than three weeks after 

 the nerve is cut. When regeneration occurs, the nerves return 

 approximately to their previous composition. 



It has also been shown that in spinal cords in which a unilateral 

 degeneration of the pyramidal tract has been produced by a lesion 

 in the opposite cerebral hemisphere, there is a similar increase of 

 water and diminution of phosphorus on the degenerated side. 

 Further, in a divided nerve Noll has shown that the phosphorised 

 material also diminishes somewhat in the central end, due to 

 "disuse atrophy." 



This disappearance of phosphorus must be due to the break-up of 

 phosphatides, and the liberation of phosphoric acid which is carried 

 away as phosphates by the lymph and blood. 



The staining reactions of a degenerated nerve also indicate that 

 the appearances are not only due to a breakdown in an anatomical 

 sense, but in a chemical sense also. Of these staining reactions the 

 one most often employed is that which is associated with the name 

 of Marchi. This is the black staining which the medullary sheaths 



