614 EVOLUTION OF HEAT, LIGHT, AND ELECTRICITY. 



the accumulation of that decomposing organic matter in the blood which it is 

 the special office of these glandulse to eliminate. Hence the due maintenance 

 of health requires that this excretion should be promoted by the use of the 

 natural and appropriate means just referred to; and this is the more necessary, 

 when from any cause the function of the kidneys is imperfectly performed. 

 There are many diseased states, moreover, in which there appears to be a special 

 determination of the materies morbi to the skin ; and in which, therefore, the 

 use of means that promote the cutaneous excretion constitutes the most efficient 

 method of eliminating them from the blood. 1 



CHAPTEE XIII. 



EVOLUTION OP HEAT, LIGHT, AND ELECTRICITY. 



1 . General Considerations. 



649. THE series of Nutritive operations which has now been passed in review 

 has been shown to consist in the continual appropriation, by the Animal organ- 

 ism, of certain " organic compounds" or " alimentary materials," which have 

 been generated for its use by Plants ; and in the constant restoration of their 

 elements to the Inorganic world, either in the very same forms of combination 

 in which they originally existed there, or as products of incipient decay, by 

 whose further decomposition those simple binary compounds will be reproduced. 

 And thus, so far as the material components of the Organic Creation are con- 

 cerned, the agency of Vegetable life is concerned in withdrawing them from the 

 Mineral world, and that of Animal life in returning them to it, after they have 

 served their purpose in the living structure. But if we examine into the source 

 of those active powers or " forces," on whose operation every change, no less in 

 the organized body than in what is commonly designated as "inert" matter, is 

 dependent, we shall find that they are all traceable to the solar radiations. It 

 is by the action of the Light and Heat of the Sun upon the Vegetable germ, 

 that it is enabled to exercise its wonderful transforming capacity, whereby it 

 extracts carbon, hydrogen, nitrogen, and oxygen from the carbonic acid, water, 

 and ammonia furnished by the atmosphere or the soil ; and that it converts these 

 into the albuminous, saccharine, and oleaginous compounds, which are the des- 

 tined food of Animals. And it is under the influence of Heat chiefly derived 

 from the same source, that the greater number of tribes of Animals are enabled 

 to apply these compounds to the purposes of organization; and that, through 

 the peculiar instruments thus constructed, those various kinds of Vital force are 

 evolved, whose operations are so different from any which we witness in the 

 Inorganic world. Accordingly, we observe that the "rate of life" in this larger 

 proportion of the Animal kingdom is regulated, as in Plants, by the amount of 

 Heat supplied to the organism from external sources ; and that, when the ex- 



1 The practical value of active diaphoresis in many febrile diseases is well understood 

 by the native practitioners among the Negroes of the Guinea Coast; who, according to Dr. 

 Daniell (Medical Topography, and Native Diseases of the Gulf of Guinea, pp. 119-20) 

 make use of it most successfully in the treatment of adynamic remittent fevers. Dr. 

 Daniell states that having himself had abundant experience of its efficacy, he has no doubt 

 of its superiority in these cases to the ordinary practice of venesection, saline purgatives, 

 large doses of calomel, &c. And he has repeatedly stated that one great secret of pre- 

 serving health in tropical climates lies in due attention to the cutaneous functions. 



