CHAPTER IV 



ACTION OF MOLAR AGENTS UPON PROTOPLASM 



THIS subject is so ill-defined that it is impossible to draw 

 any line of distinction between contact on the one hand and 

 a crushing pressure, or wounding, on the other. The molar 

 agents may be solid or fluid. The methods of application may 

 vary from a blunt contact or a sharp cut or puncture to the 

 impact of flowing liquid. All these agents have this in common, 

 however, that they act in a gross, mechanical way. The sub- 

 ject will be discussed under the following heads : (I) The 

 effect of molar agents upon lifeless matter ; (II) effect upon 

 the metabolism and movement of protoplasm; and (III) effect 

 in determining the direction of locomotion, - - thigmotaxis 

 (stereotaxis) and rheotaxis. 



1. EFFECT OF MOLAR AGENTS UPON LIFELESS MATTER 



Mechanical disturbance can induce in certain lifeless com- 

 pounds violent chemical changes. Compounds which are so 

 affected are preeminently unstable. This instability, however, 

 varies greatly in degree. In some cases, the blow of a hammer 

 is required to upset the molecules ; the result being often a 

 violent explosion. In other cases (e.g. chloride or iodide of 

 nitrogen), the slightest touch of a feather suffices to produce 

 an explosion. Now, most of the substances which explode 

 upon impact, and which are used in the arts, are organic com- 

 pounds, fulminate, nitro-glycerine, gun-cotton, and picric- 

 acid derivatives, and therefore it is not surprising that we 

 find the notoriously unstable protoplasm violently affected by 

 contact. 



Especially important for biology is the fact that undulatory 



motions and other periodic disturbances produce very important 

 H 97 



