INTROD.] THEORIES OF LIFE. 2L 



So much for the dependence of Life and Organization on a con- 

 trolling and directing Entity. The sagacity of John Hunter led 

 him to reject this doctrine entirely; but, as he completely passed 

 over the influence of the natural agencies of inorganic nature upon 

 organized beings, he was forced to assume the presence of a peculiar 

 material substance, pervading and giving vital properties to solids and 

 fluids : yet such a constituent of the body ought to be demonstrable 

 by chemical or other means. It is clear that this materia vitce can- 

 not be, as Mr. Abernethy suggested, electricity, or anything akin to 

 it. Electricity requires for its development the reciprocal action of 

 different kinds of matter, and it is abundantly evolved in various 

 animal processes, as a necessary result of chemical laws. If, there- 

 fore, organization and vital actions depended upon electricity, this 

 agent would, at once, be formed by, and direct the formation of, 

 each organism. 



Mere composition of matter does not give life, says Hunter ; if 

 he had added, that organized bodies acted on by, and co-operating 

 with, certain vital stimuli developed vital actions, there would have 

 been no need for the assumption of a materia vitas. The resistance 

 which living animals introduced into the stomach are capable of 

 affording to its solvent powers, and the digestion of the walls of the 

 stomach by its own fluid after sudden and violent death, seemed to 

 denote that the dead animal, or dead stomach, had lost a something 

 which previously protected them against the influence of the gastric 

 fluid. But this is no more than a case familiar to chemists, viz. the 

 influence of a stronger affinity controlling a weaker. When iodide 

 of potassium is mixed with a solution of starch, no change ensues ; 

 but, if a minute quantity of chlorine be added, a blue iodide of starch 

 is instantly formed : the superior affinity of the iodine for the potas- 

 sium hindered the union of the former with the starch; but, as soon 

 as the iodine was set free by the stronger attraction between the 

 potassium and the chlorine, it speedily united with the starch. So, 

 in the living animal, the affinity of its component particles for each 

 other is greater than their affinity for the gastric fluid ; but in the 

 dead animal the former affinity is destroyed, the latter comes into 

 play. Whether is it more philosophical to assume the removal of a 

 particular agent, for which removal no cause can be assigned ; or, 

 to state the simple fact of the physical difference between dead and 

 living organic matter? 



II. It is very difficult to define a precise boundary between the 

 vegetable and animal kingdoms. The lowest animals exhibit so 

 much of the plant-nature, that naturalists are as yet undecided as 



