COMPOSITION OF BODIES. 3 



beg still further to trespass upon your attention by reminding 

 you briefly of the special province of chemical science, and the 

 special character of chemical phenomena. 



(2.) If we examine any ordinary plant or animal, we find in it 

 a great number of parts or organs root and stem, and bark and 

 leaves, and flowers and fruit, or bones and ligaments, and muscles 

 and viscera, and nerves and vessels. If we examine any one of 

 these parts more minutely, we find that it also is made up of 

 parts differing from one another, and so disposed towards one 

 another as to present evidence of arrangement or organisation. 

 Proceeding a little further, we find that each of these parts has a 

 definite composition, and that the composition of the different 

 parts is, to some extent, at any rate, independent both of their 

 individual structure and mutual co-ordination. We find, for in- 

 stance, very differently characterised tissues composed mainly of 

 fibrin or albumen, others of gelatin or chondrin, others of fat, 

 and others, again, of phosphate of lime. Now, chemistry does 

 not concern itself at all with the structure and arrangement oi 

 parts, but treats only of their composition. It distinguishes 

 between the different kinds of matter of which all bodies whatso- 

 ever are composed, whether living or dead, structural or structure- 

 less, mineral or organic. In particular, it teaches us as physicians 

 the composition of every tissue and fluid of the human body, 

 and of every external agent by which that body is affected the 

 air we breathe, the water we drink, the food by which we are 

 nourished, the medicines by which we are healed, and the 

 poisons by which we are destroyed. 



(3.) But a knowledge of the composition of bodies is, after all, 

 only the statical or secondary object of chemical inquiry ; for, in 

 common with physics, chemistry has primary reference to the 

 varied existence of matter in time, and to the series of changes 

 which it manifests. We have regard to a body not only as it now 

 is, but as it has been, as it may hereafter be, the changes it has 

 undergone in time past, the changes which it may undergo in 

 time to come. Confining our attention to a single object this 



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