496 GENERAL PHYSIOLOGY 



Moses and Aaron performed before the Egyptian Pharaoh more 

 than three thousand years ago, belong in this category. By slight 

 pressure in the neck-region it is possible to make a wildly excited, 

 hissing, erect asp (hooded snake) suddenly motionless, so that the 

 dangerous creature can be put into any desired position without 

 fear of its fatal bite (Fig. 245, /). The well-known experimentum 

 mirahile de iviaginatione gcdlinae of Father Kircher depends upon 

 the same causes. If an excited fowl be seized suddenly with a firm 

 grip and laid carefully upon its back, after a few brief attempts to 

 escape it lies motionless (Fig. 245, 11). Guinea-pigs (Fig. 151, 

 p. 358), rabbits, pigeons, frogs, lizards, crabs and numerous other 

 animals behave similarly. The hypnosis of human beings depends 

 likewise essentially upon inhibition of the activity of the ganglion- 

 cells in the cerebral cortex, in common language upon an inhibition 

 of the will, and in sleep the inhibition of the activity of all the higher 

 brain-centres is evident. These cases do not depend upon depression; 

 the stimuli that act as causes of them are too feeble. We must 

 recognise in them, as in numerous other phenomena of inhibition, 

 the other case, i.e., the inhibition of an existing excitation by the 

 excitation of antagonistic components of biotonus in the partici- 

 pating ganglion-cells. 



It will be a promising task of the future to investigate system- 

 atically interference-reactions and to ascertain their relations to 

 the interesting processes in the central nervous system. 



3. Polojr Changes of Biotonus and the Mechanism of Axial Orientation 

 upon Unilateral Stimulation 



Thus far we have considered merely the changes of biotonus 

 that are caused by general stimulation of living substance. But 

 the changes that result from local stimulation are worthy of 

 attention, because in certain cases they give rise to very charac- 

 teristic external effects. These are the directive effects of stimuli 

 upon motile organisms, which we have become acquainted with as 

 chemotaxis, barotaxis, thermotaxis, phototaxis and galvanotaxis. 

 These interesting phenomena are called out, as has been seen, by 

 the unilateral, or unequal, action of stimuli upon the activity of 

 contractile elements. In other words, all these cases of stimulation 

 depend upon changes in those members of the biotonic series A 

 and D, that mediate the contraction and expansion of contractile 

 elements. A movement in a definite direction can take place only 

 where differences as regards contraction or expansion exist in 

 two different parts of the cell-bod}'. Since, as regards the motor 

 effect, contraction (c) and expansion (c) are two antagonistic phases 

 of the movement, we can express the mutual relation of these two 

 members of biotonus by a fraction in a manner analogous to that 

 of the expression of biotonus itself, without, however, at the same 



