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 

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