SI PHILOSOPHY OF ZOOLOGY. 



obtained, may be regarded in many cases as modifications 

 of the elements of the substance, occasioned by the process- 

 es employed, rather than the display of the number or na- 

 ture of the ingredients as they existed previous to the ana- 

 lytical operations. Errors, we know, are to be guarded 

 against in the analysis of mineral waters, arising from com- 

 binations taking place during the process, which did not 

 exist in the compound previous to analysis*. How much 

 more necessary is it, to exercise caution in drawing 

 our conclusions regarding the composition of animal bo- 

 dies ? 



In this section I shall enumerate the elementary bodies, 

 which are considered as entering into the composition of the 

 parts of animals, and then consider the combinations which 

 these form, or the substances in which they have been 

 detected. 



I. ELEMENTARY SUBSTANCES. 



1. Carbon. This substance exists in various states of 

 combination, in the fluids as well as the solids of every ani- 

 mal. It has never been detected in a separate state in any 

 animal substance. In the lungs, however, it appears to 

 occur in the form of charcoal, according to the observations 

 of Dr PEARSON -f-. The lungs, in youth, are light colour- 

 ed ; but they increase in darkness with age, and in old 

 persons they are nearly black. This change of colour is 

 produced, by the deposition of charcoal in the cells of the 

 lungs, and the bronchial glands. Dr PEAHSON considers 



* See Dr MURRAY'S valuable paper, " An Analysis of Sea-water." 

 Edin. Trans, vol. viii. p. 205 



t '* On the Colouring Matter of the Black Bronchial Glands, and of the 

 Black Spots of the Lungs." Phil. Trans. 1813, p. 159. 



