INTERFERENCE OF EXCITATIONS 305 



shrouded in darkness, has gradually in the course of years been 

 completely elucidated. 



Before going back to the cases of inhibition and explaining 

 them by this general principle, it is necessary that we penetrate 

 more deeply into the details of the characteristic course of the 

 refractory period. By this means we will find the conditions 

 which universally determine the interference in the effects of 

 stimulation. 



First of all, it is self-evident that the occurrence of interference 

 of stimulation in a living system can only take place when the 

 succeeding stimulus is applied before the effects of the previous 

 one have completely disappeared. Within the interval, however, 

 which is involved from the moment of the beginning of a stimulus 

 until its effect disappears through the self-regulation of metab- 

 olism, there is the possibility of various interference results from 

 stimulation. 



If we take into consideration the various instances which can 

 arise, perhaps we may best start with that type wherein the first 

 stimulation produces depression, whereas the second has an excit- 

 ing effect on disintegration. In this type the response to the 

 second stimulus is weaker than when the second stimulus alone 

 is applied. As a concrete example of this type, we may refer to 

 the interference of an induction shock in a nerve during the 

 relative want of oxygen. We arrange a nerve of a nerve muscle 

 preparation of a frog in a glass chamber, as already described, and 

 determine the threshold of stimulation of the stretch within the 

 chamber by the weakest induction shocks which produce response. 

 The oxygen is then removed and the effect on the threshold de- 

 termined. As shown by Baeyer it is found that with increasing 

 asphyxia the threshold of stimulation for induction shocks be- 

 comes continually higher. The irritability is likewise decreased. 

 This occurs, as the investigations of Lodholz show, at first slowly, 

 then more and more rapidly. The curve of the decrease of irri- 

 tability has a logarithmic form. During the continuation of the 

 depressing stimulus, i.e., the want of oxygen, the exciting stimulus 

 has less and less effect. If oxygen is again brought in contact 

 with the nerve, irritability immediately returns to its original 



