MUSCLE AND NERVOUS TISSUE 



203 



non-phosphoriscd fat has been absorbed. This absorption occurs earlier in 

 the peripheral nerves than in the central nervous system. The non-phos- 

 phorised fat of degenerated myelin is also either richer in olein, or the olein 

 is more loosely combined than in the healthy medullary sheath; hence 

 the deeper reaction with osmic acid even in the presence of chromic acid 

 as in the March! test. The following table gives details of these experi- 

 ments : 



The foregoing figures relate to the peripheral portions of the nerves. Noll 

 has also shown that the phosphorised fat diminishes somewhat in the central 

 ends of cut nerves due to ' disuse atrophy.' 



Further, it has been found that in human spinal cords in which a unilateral 

 degeneration of the pyramidal tract has been produced by a lesion in the 

 opposite hemisphere, and which gives the Marchi reaction, there is a similar 

 increase of water and diminution of phosphorus on the degenerated side. 



Cerebro-spinal Fluid. This plays the part of the lymph of the central 

 nervous system, but differs considerably from all other forms of lymph. It 

 is a very watery fluid, containing, besides some inorganic salts similar to 

 those of the blood, a trace of protein matter (globulin) and a small amount 

 of a reducing substance, the nature of which was for a long time uncertain 

 but which seems now to have been proved to be sugar. It contains the 

 merest trace of choline ; but this is not devoid of significance, for this fact 

 taken in conjunction with another namely, that physiological saline solution 

 will extract from perfectly fresh nervous matter a small quantity of choline 

 shows us that lecithin is not a stable substance, but is constantly breaking 

 down and building itself up afresh; in fact, undergoing the process called 

 metabolism. This is most marked in the most active region of the brain 

 viz. the grey matter. 



