532 



METABOLISM OF NERVES. 



Reaction. Nervous substance, when passive, is neutral or feebly alkaline in 

 reaction, while active (? and dead) it is acid (Funke). The grey matter of the 

 brain, when quite fresh, is alkaline (Liebreich), but death rapidly causes it to 

 become* acid (Gscheidlcn). 



The reaction of nerve-fibres varies during life. After introducing methyl-blue into the 

 body of a living animal, Ehrlich found that the axis-cylinder became blue, i.e., in those nerves 

 which have analkaline reaction (cortex cerebri, cardiac, sensory, motor (nou-stnped), gustatory 

 and olfactory fibres), while the termination of motor (voluntary) nerves remained uncoloured. 

 The latter he regards as acid. 



The nerves after death have a more solid consistence, so that in all probability 

 some coagulation or change, comparable to the stiffening of muscle, occurs in them 

 after death, while at the same time a free acid is liberated ( 295). If a fresh 

 brain be rapidly "broiled" at 100 C, it, like a muscle similarly treated, remains 

 alkaline ( 295). 



In 100 parts of ash, Breed found potash 32, soda 11, magnesia 2, lime 0*7, NaCl 5, iron 

 phosphate 1*2, fixed phosphoric acid 39, sulphuric acid 0*1, silicic acid 0*4. 



[Ptomaines ( 166) are obtained from putrefying brain. They have an effect on the motor 

 nerves like curara, but in much less degree, while the phenomena last for a much shorter time 

 {Ouarcschi and Mosso).] 



Mechanical Properties. One of the most remarkable mechanical properties of 

 nerve-fibres is the absence of elastic tension according to the varying positions of 

 the body. Divided nerves do not retract; such nerves exhibit delicate, microscopic, 

 transverse folds, [like watered silk] or Fontana's transverse markings. 



The cohesion of a nerve is very considerable. When a limb is forcibly torn 

 from the body, as sometimes happens from its becoming entangled in machinery, 

 then erve not unfrequently remains unsevered, while the other soft parts are 

 ruptured. [Tillaux found that a weight of 110 to 120 lbs. was required to rupture 

 the sciatic nerve at the popliteal space, while to break the median or ulnar nerve 

 of a fresh body, a force equal to 40 to 50 lbs. was required. The toughness and 

 elasticity of nerves are often well shown in cases of injury or gun-shot wounds. 

 The median or ulnar nerve will gain 15 to 20 centimetres (6 to 8 inches) before 

 breaking. Weir Mitchell has shown that a healthy nerve will bear a very consider- 

 able amount of pressure and handling, and, in fact, the method of nerve-stretching 

 depends upon this property of a nerve-trunk.] 



323. METABOLISM OF NERVES. Influence of Blood-Supply. We know 



very little regarding the metabolic processes that occur in nerve-tissue. Some 

 extractives are obtained from nerve-tissue, and they may, perhaps, be regarded as 

 decomposition-products (p. 531). It has not been proved satisfactorily that during 

 the activity of nerves there is an exchange of O and C0 2 . That there is an 

 exchange of materials within the nerves is proved by the fact that, after com- 

 pression of the blood-vessels of the nerves, the excitability of the nerves falls, 

 and is restored again when the circulation is re-established. Compression of the 

 abdominal aorta causes paralysis and numbness of the lower half of the body, 



