CHAPTER IV 



ACTION OF MOLAR AGENTS UPON PROTOPLASM 



This subject is so ill-defined that it is impossible to dra^ 

 any line of distinction between contact on the one hand an 

 a crushing pressure, or wounding, on the otlier. The mols 

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

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

 impact of flowing liquid. All these agents have this in commoi 

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

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

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

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

 in determining the direction of locomotion, — thigmotax: 

 (stereotaxis) and rheotaxis. 



§ 1. Effect of Molae Agents upon Lifeless Matte 



Mechanical disturbance can induce in certain lifeless con 

 pounds violent chemical changes. Compounds which are s 

 affected are preeminently unstable. This instability, howeve 

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

 is required to upset the molecules ; the result being often 

 violent explosion. In other cases Qe.g. chloride or iodide c 

 nitrogen), the slightest touch of a feather suf&ces to produc 

 an explosion. Now, most of the substances which explod 

 upon impact, and which are used in the arts, are organic con 

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

 acid derivatives, — and therefore it is not surprising that w 

 find the notoriously unstable protoplasm violently affected b 

 contact. 



Especially important for biology is the fact that undulator 

 motions and other periodic disturbances produce very importar 

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