198 IRRITABILITY 



simple, and in part very complex states. It now behooves us to 

 obtain a general understanding of interference action, to learn 

 the fundamental laws in connection with these complex actions, 

 to shell out, as it were, the general factors involved in the special 

 conditions. In this connection the examples already referred to 

 furnish all of the data necessary for our first orientation. In the 

 simple instance in which the effect of galvanic stimulation was 

 augmented by increase of temperature and again in the case where 

 there was a diminution of excitation resulting from the alcohol, 

 the interference of the two stimuli is consequent upon the 

 the fact that the location of attack is the same. The constant 

 current acts upon a portion of the infusorium, which also re- 

 sponds to elevation of temperature. We have a real, or, as I 

 may term it, "homotopic interference," for it is an interference 

 in which the general point of attack is the same for both stimuli. 

 In contradistinction to this case, we have the examples of the 

 interference of thigmotaxis and galvanotaxis in the hypotrichous 

 infusoria. Here the effect of interference, the characteristic 

 position of the axis of the cell body, is brought about by the fact 

 that the galvanic stimulus affects different elements than the 

 mechanical. The turning of a creeping Stylonychia or Urostyla, 

 when the current is closed, in which the anterior portion of the 

 body was previously directed towards the anode, results from 

 excitation of the perioral cilia from the anodic pole. The me- 

 chanical stimulation, on the contrary, exerts its effect upon the 

 locomotion and border cilia. Only when there is a turning of 

 the anterior portion of the body towards the anode, would the 

 galvanic stimulus affect also the anterior locomotion cilia and 

 thereby counteract turning towards the anode. Therefore, we 

 have before us in this case of the assuming of a characteristic 

 position of the axis of the cell body the expression of an apparent, 

 or, as I prefer to express it, a "heterotopic interference," in which 

 the two stimuli do not actually interfere in their action, but rather 

 influence the final result, in that the condition for the state of 

 the system in its totality is dependent upon its individual com- 

 ponents. This heterotopic interference is of particular imf)or- 

 tance in the bringing about of the movements of the living system. 



