THE PROCESS OF EXCITATION 101 



tability decreases upon the withdrawal of oxygen. In this con- 

 nection I should like to cite some particularly significant instances. 



During a sojourn at the Red Sea in 1894-95 I was able to 

 establish this dependence in the single-celled organism, the Rhizo- 

 plasma Kaiseri, a large naked orange-colored rhizopod. (Figure 

 10, A.) Mechanical stimulation, which under normal vital con- 

 ditions of these organisms brings about contraction in the long- 

 branched pseudopods, becomes inefifective with a cessation of the 

 movement of protoplasm, when oxygen is removed and is replaced 

 by a stream of hydrogen. (Figure 10, B.) With renewed intro- 

 duction of oxygen there is a return of the protoplasmic movement 

 and entire recovery takes place. 



This dependence of irritability upon oxygen is most clearly 

 demonstrated in the nerve centers. For this purpose I have 

 employed the spinal cord of the frog.^ A canula is introduced 

 and fixed into the aorta of the animal and the blood is replaced 

 by a current of oxygen-free saline solution. The centers of the 

 spinal cord are thereby wholly isolated from the supply of oxy- 

 gen. The indicator for the irritability here used is reflex exci- 

 tation from the skin to the gastrocnemius, or better, stimulation 

 of the central stump of the sciatic nerv^e with single induction 

 shocks, bringing about reflex response of the triceps. The reflex 

 may be considerably augmented by increasing the reflex excita- 

 bility of the spinal cord by poisoning the animal with strychnine. 

 On testing the reflex excitability at the beginning of the experi- 

 ment it will be found that the reaction to each individual stimulus 

 consists, in consequence of the strychnine poisoning, of a long- 

 continued maximal tetanus. The longer the deficiency of oxygen 

 continues, the briefer become the tetanic reflex contractions fol- 

 lowing a single stimulus. Soon reflex tetanic responses are 

 merely short single contractions, which decrease more and more 

 with the continuance of oxygen deficiency. Finally, the same 

 stimuli which previously produced strong tetanic contractions 

 of long duration are altogether without effect. Although by 



1 Max Verworn : "Ermiidung Erschopfung und Erholung der nervosen Centren 

 des Riickenmarks. Ein Beitrag zur Kenntniss der Lebensvorgange in den Neuronen." 

 Archiv. f. Anat. u. Physiologie. physiol. Abteil. 1900 Suppl. 



The same: "Ermiidung und Erholung." In Berliner Klin. Wochenschrift 1901. 



