102 IRRITABILITY 



increasing the intensity of stimulation brief contractions can 

 again be brought about, irritability decreases more and more, 

 until at last even the strongest stimuli remain without result. 

 If the oxygen-free saline solution is now replaced by one satu- 

 rated with oxygen, or blood of the ox, rendered arterial, the 

 excitability returns within a few minutes and soon reaches the 

 maximal height which it possessed under the influence of the 

 strychnine poison. Even the weakest single stimuli now again 

 produce tetanus. The same process reoccurs, if the fluid used 

 for transfusion containing oxygen is again replaced by an oxygen- 

 free saline solution. In this way, by repeated change of the per- 

 fusing fluid, we can demonstrate in the most positive manner this 

 alteration in irritability, the result of the alternate presence and 

 removal of oxygen. This is perhaps the best example of the 

 close dependence of irritability on oxygen. 



This same fact can be observed with equal clearness in the 

 nerve. At my suggestion H. v. Baeyer 1 showed as the result of 

 investigations made in the Gottingen laboratory the dependence 

 of irritability of the nerve upon oxygen for the first time. By 

 employing as the method the ascertainment of the threshold of 

 stimulation I then made a closer study of the alterations in irrita- 

 bility during asphyxiation. These observations were soon after 

 continued by Frohlich. 2 The method is as follows : the nerve of 

 a nerve-muscle preparation of the frog is drawn through a glass 

 chamber which is made completely air-tight and containing plati- 

 num electrodes. The air in the chamber is then displaced by a 

 stream of pure nitrogen. (Figure 11.) On testing that part 

 of the nerve situated within the glass chamber with single break 

 induction shocks it can be observed that its irritability, measured 

 by the threshold of stimulation for muscle contraction, decreases 

 more and more, until after the lapse of some hours, the stimula- 

 tion required is so strong as to reach the region of the "Strom- 

 schleifengrenze." If in place of the stream of nitrogen, air or 

 pure oxygen is now allowed to flow through the chamber, the 



1 H. v. Baeyer: "Das Sauerstoffbediirfniss des Nerven." Zeitschrift f. allgemeine 

 Physiologic Bd. II, 1903. 



2 Fr. W. Frohlich: "Das Sauerstoffbediirfniss des Nerven." Zeitschrift f. allgem. 

 Physiologic Bd. Ill, 1904. 



