ON THE NATURE OF LIFE. 193 



of the particles of the solvent, produces decomposition 

 of the complex and delicate living molecules and their 

 death, just as mechanical force of any other kind, such 

 as pressure, blows, tearing, &c. Although a large pro- 

 portion of water must be contained by imbibition in 

 the living matter, yet a certain proportion cannot be 

 exceeded without injury. Accordingly, the living 

 matter is always protected from the solvent action of 

 pure water either by cell walls or by being kept 

 bathed by fluids not so strongly diffusible, as is always 

 the case in the higher animals. Pure distilled water, 

 in fact, is rapidly fatal to protoplasm when placed in 

 contact with it,* inducing death and consequent coagu- 

 lation. In the lowest tribes, which are chiefly aquatic, 

 such as the infusoria, when they consist of apparently 

 nothing but a naked lump of protoplasm, no doubt, 

 this substance is so constituted, as to repel excess of 

 water and prevent diffusion and solution. No com- 

 parison with the physical state of dead matter can give 

 a correct idea of that of living matter as we see it in 



the amcebse and other rhizopoda. The slow crawlino- 



- 



movement, the rapid pouring out of the substance in one 



direction, and, again, the gathering up of the whole 

 mass into a ball, in short, the numberless changes of 

 shape without change of volume, show a mobility 

 almost equal to liquids, with a cohesive power like a 

 solid, and in fine physical properties, possessed by no 

 other substance. This very peculiarity of the living 

 matter viz., that it is always semifluid, transparent 



* '' The plasma usually appears as a semi-fluid, albuminous body, 

 of the consistence of a tough, sticky, thread-drawing mucilage, which 

 is insoluble in water, and even, in many cases, coagulates by the access 

 of water" (Huckel, " Gen. Morphol.," i. 278). 



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