194 Comparative Physiology. 



cessaiy." On this head he afterwards quotes Sir J. Herschel's 

 demonstration, that a force 50,000 times that of gravity may be 

 instantaneously generated by the action of galvanism on an 

 amalgam of mercury, with a millionth part of its weight of 

 sodium ; thus showing that the minutest mixture of ingredients 

 may completely reverse the electrical, and conseqviently the che- 

 mical relations of large masses of organised matter. " The 

 bulk of the inorganic world is made up of the metals and their 

 compounds ; while the essential ingredients of living bodies are 

 the non-metallic elements, oxygen, hydrogen, nitrogen, and car- 

 bon ; carbon being the most characteristic in vegetables, and 

 nitrogen in animals. Chemical affinity, the result of the elec- 

 trical properties of bodies, is affected by temperature ; the 

 affinities of potassium and iron to oxygen are reversed by 

 different states of temperature. A distinct set of vital affini- 

 ties can hardly be distinguished from chemical, by saying that 

 all organic substances decompose upon the loss of vitality. It 

 is, therefore, scarcely a proper definition of life, to say that it is 

 the power by which decomposition is resisted; it is rather the 

 provision for the removal of particles in a state of incipient 

 decay, and their replacement by others freshly united. Car- 

 bonic acid, the first product of putrefaction, is the substance 

 given off most copiously during life, as well as death ; the inter- 

 stitial or lymphatic replacement fidly compensates for the ten- 

 dency to decay ; if this is prevented, decomposition and loss of 

 vital properties ensue." 



It appears, therefore, he considers the power of life to consist 

 more in the insterstitial displacement of decayed and replacement 

 of sound particles, than in the prevention of decomposition, be- 

 cause inorganic substances are also acted on differently in differ- 

 ent circumstances. It is not clear, however, that the tendency 

 to decom230se is not much greater after dissolution than before ; 

 the removal of decayed particles preventing accumulation will 

 not, perhaps, account for the much less tendency to decompose 

 during life. After death, all the particles, both sound and 

 decayed, appear to be more acted on by chemical affinity ; and 

 hence the general opinion that vitality furnishes a resisting as 

 well as replacing power. The waste of the body producing 

 decay may be distinguished from chemical affinity, having a 

 power of displacing the weakened decayed particles, which it 

 does not possess over the sound ones ; and may thus be pre- 

 vented, by vital force maintaining the sound parts in a con- 

 dition capable of resisting chemical action, from interfering with 

 them, while it removes all those particles become unsound from 

 waste. The carbonic acid given off by animals will be partly 

 also from substances not assimilated ; perhaps partly so in 

 plants also. The power which enables living bodies to with- 



