INTRODUCTION. 11 



The relations of vegetables and animals to the surrounding atmos- 

 phere are therefore in an inverse ratio the former reject water and 

 carbonic acid, while the latter produce them. The essential function of 

 the animal body is respiration ; it is that which in a manner animalises 

 it ; and we shall see that the animal functions are the more completely 

 exercised, in proportion to the greatness of the powers of respiration 

 possessed by the animal. This difference of relations constitutes the 

 fourth character of animals. 



OF THE FORMS PECULIAR TO THE ORGANIC ELEMENTS OF THE 

 ANIMAL BODY, AND OF THE PRINCIPAL COMBINATIONS OF ITS 

 CHEMICAL ELEMENTS. 



An areolar porous tissue and three chemical elements are essential to 

 every living body ; there is a fourth element peculiarly requisite to that 

 of an animal ; but this tissue is composed of variously formed meshes, 

 and these elements are variously combined. 



There are three kinds of organic materials or forms of texture, the 

 cellular membrane, the muscular Jibre, and the medullary matter, and 

 to each form belongs a peculiar combination of chemical elements, as 

 well as a particular function. 



The cellular substance is composed of an infinity of small fibres and 

 laminae, fortuitously disposed, so as to form little cells that communicate 

 with each other. It is a kind of sponge, which has the same form as 

 the body, all other parts of which traverse or fill it, and contracting 

 indefinitely on the removal of the causes of its tension. It is this power 

 that retains the body in a given form and within certain limits. 



When condensed, this substance forms those laminae called mem- 

 branes; the membranes, rolled into cylinders, form those more or less 

 ramified tubes named vessels; the filaments called Jibres are resolved 

 into it, and bones are nothing but the same thing indurated by the 

 accumulation of earthy particles. 



The cellular substance consists of a combination well known as 

 gelatine, characterised by its solubility in boiling water, and forming, 

 when cold, a trembling jelly. 



We have not yet been able to reduce the medullary or cerebral matter 

 to its organic particles ; to the naked eye, it appears like a soft whitish 

 pulp, consisting of excessively small globules ; it is not susceptible of any 

 apparent motion, but in it resides the admirable power of transmitting ta 

 the mind the impressions of the external senses, and conveying to the 



