12 PHYSIOLOGY. 



the quantity and quality of the aliment taken in, by the powers 

 of concoction and assimilation, by the circumstances of applica- 

 tion and concretion, or by certain preternatural matters carried 

 along with it. 



XVIII. The external matter that may be insinuated into 

 the simple solid, is various, but, for the most part, is only aque- 

 ous moisture in greater or less quantity. 



XIX. That these several causes may affect the proportion 

 of water in the simple solid, and thereby give a different state 

 of it, is sufficiently obvious. That the same causes may also 

 affect the other concreting matter, we can, in general, perceive 

 to be possible ; but in what manner, or upon what occasions 

 they do so, is not easily discerned. 



XX. The properties of the simple solid (VIII.) maybe also 

 varied by its state of aggregation; and this again may be varied, 

 1. By the temperature of the atmosphere to which the body is 

 long exposed. 2. By the pressure, external or internal, which is 

 applied to the solid. 3. By the degree of extension of the solid 

 beyond its natural state, which, in every living body, is given 

 more or less to every part of the soft or flexible solids ; and, 

 lastly, by the motion or rest to which the solid is accustomed. 



XXI. The properties (VIII.) of the solid parts are also 

 varied by the state of their organization. This every where de- 

 pends upon an arrangement of fibres, the state of cellular tex- 

 ture, or upon a texture of vessels ; and, therefore, to explain the 

 different states of organization, it will be enough to mention the 

 causes of the differences which occur in these fundamental parts. 



XXII. Fibres may differ in size by the several causes 

 (XIV. XXI.) affecting the mixture and aggregation of the 

 matter of which they are formed, and by these causes alone ; 

 but how far the organization of any part depends upon an ar- 

 rangement of fibres, we cannot distinctly perceive ; and, if it 

 does, we cannot perceive that the state of such parts differs 

 otherwise than by the state of the cellular texture every where 

 interposed between the supposed fibres. 



XXIII. The state of cellular texture is a most important 

 circumstance in all organized parts ; and it may be varied by 

 many different causes. 1. The texture may be more dense, and 

 thereby firmer, as it has been more pressed by the actions of 



