THE NERVES 353 



KOFER'S brain weighed 1320 gm. HELMHOLTZ'S, 1900 gm.) ; for 

 sickness, age, etc., may produce considerable changes in a brain's 

 capacity to hold water, so that the brains of men offer no basis for 

 post mortem comparison. 

 MASUDA supplied the following figures: 



1st Man 2nd Man 



Weight of brain 1,291 gm. 1,133 gm. 



Dried substance 176,36 " 260,30 " 



1 gm. of dried substance contains water. ... 6,14 " 3,55 " 



With the same aqueous content as Brain II, Brain I would have 

 weighed 767 gm. With the same aqueous content as Brain I, Brain 

 II would have weighed 1858 gm. There are increasing indications 

 that colloid investigation is destined to carry nearer to solution the 

 old problem of nerve irritability. 



Nerve Irritability and Swelling. 



In considering muscle function we have seen that it is associated 

 with a certain condition of swelling (see p. 294). The like is also 

 true of nerves. The nerves lose their irritability when placed in iso- 

 tonic solutions of cane sugar or other nonconductors and recover it 

 again when they are placed in physiological salt solution (MATHEWS,* 

 E. OVERTON * 4 ). Various other neutral salt solutions also injuriously 

 affect the irritability of nerves in accordance with a lyotropic series. 

 The arrangement given by various authors (MATHEWS, P. VON 

 GRUTZNER) is not as unequivocal as for muscle. We must remember 

 that the methods of investigation were not the same as for muscle, 

 and that the penetration of the salt solution to the axis cylinder 

 through the lipoid insulating layer was not as uniform. R. HOBER * 3a 

 (p. 307) summarizes the depressant action of ions on nerve irrita- 

 bility in the following series: 



Na < Li < Cs < NH 4 < Rb < K 

 S0 4 <Cl<Br<I 



The anion series is the reverse of that for muscle irritability. 

 We know that in the precipitation of acid albumin, the lyotropic 

 series is the opposite of that for alkali albumin; we know further that 

 contracting muscle has an acid reaction; on this account we may with 

 some probability infer that nerve albumin is more or less alkaline 

 (negative). 



HOBER succeeded in rendering visible the changes which reveal 

 irritability or the absence of irritability of nerves. The sciatics of 

 frogs still connected to their gastrocnemii were placed in isotonic 

 salt solution until they lost their characteristic irritability to the 



