134 



THERMAL AND CHEMICAL CHANGES IN MUSCLE [CH. XII. 



currents will completely block the transmission of impulses, and not only that, but 

 the nerve remains blocked after the current is removed. After the current has 

 been allowed to flow for two minutes the nerve remains impassable to nerve 

 impulses for an hour or more, and then slowly recovers. If, therefore, faradic 

 excitation of the nerve is kept up all this time and fails to excite the contraction of 

 the spleen after the removal of the constant current, it is impossible to say whether 



G.P. 



S 



N 



Fio. 151. Apparatus for obtaining splenic curves, s, Spleen in oncometer o, which is made of gutta 

 percha, and covered with a glass plate (G.P.) luted on with vaseline. M is the splenic mesentery 

 containing vessels and nerves ; this passes through a slit in the base of the oncometer which is made 

 air-tight with vaseline. The oncometer is connected to the flexible bellows (B) by the india-rubber 

 tube (R), the side tube (T) being closed during an experiment by a piece of glass rod. The recording 

 lever (L) writes on a revolving drum. 



this is due to fatigue of the nerve-fibres on the proximal side of the block, or whether 



it may not be due to the fact that the block (due to electrolytic changes caused 



constant current) is still effective. 



Our best results were obtained by using cold instead of a constant current as 



our blocking agent. 



Fig. 151 is an outline drawing of the apparatus used, and fig. 152 shows the 



arrangement adopted in connection with the nerve. 



The nerve (N) rests on a metal tube (T) through which 

 water can be kept flowing. E is the situation of the 

 electrodes. If the nerve is excited, the spleen con- 

 tracts, and the recording lever (in fig. 151) falls. If 

 now brine at to 2 C. is kept flowing through T, the 

 nerve impulses are blocked by the cold, and cannot 

 reach the spleen. Immediately the cold brine is re- 

 placed by warm water at 30 C., the nerve again becomes 

 passable by nerve impulses, and the spleen contracts 

 once more. 



While the fluid in T is kept at the low temperature 

 mentioned, the nerve is excited with strong induction 

 shocks all the time, and the spleen remains irre- 

 sponsive ; the nerve impulses are able to reach T but 

 not to pass it. If then warm water is passed through T, 

 and the block produced by the cold is thus removed, 

 and the spleen continues to be irresponsive, we have a 

 proof that the piece of nerve between E and T has been 

 fatigued. But our experiments have shown us that 

 non-medullated nerve is just as difficult to fatigue as 

 medullated nerve. Even after six hours' continuous 



DT 



FIG. 152. Arrangement of ap- 

 paratus in connection with 

 the splenic nerve, s is the 

 spleen, and N the main 

 bundle of nerves. The 

 nerve rests on the metal 

 tube (T) through which fluid 

 at the required temperature 

 is kept flowing, and on the 

 electrodes (E) which come 

 from the secondary coil of 

 an inductorium. 



excitation the nerve is just as excitable as it was at the start, and a full splenic 

 contraction is obtained when the cold block is removed. 



