20 INTRODUCTION. 



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 fibre., and the medullary matter., 

 and to each form belongs a peculiar combination of chemical ele- 

 ments, as vi'^ell 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 com- 

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

 forni 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 cer- 

 tain limits. 



When condensed, this substance forms those lamina called mem- 

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

 less ramified tubes named vessels; the filaments called fibres 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 tlie medullary matter to its 

 organic molecules; to the naked eye, it appears like a sort of soft 

 bouillie, consisting of excessively small globules; it is not suscepti- 

 ble of any apparent motion, but in it resides the admirable power of 

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

 conveying to the muscles the orders of the will. It constitutes the 

 greater portion of the brain and the spinal marrow, and the nerves 

 which are distributed to all the sentient organs are, essentially, mere 

 fasciculi of its ramifications. 



The fieshy or muscular fibre is a peculiar sort of filament, whose 

 distinctive property, during life, is that of contracting when touched 

 or struck, or when it experiences the action of the will through the 

 medium of the nerve. 



The muscles, direct organs of voluntary motion, are mere bundles 

 of fleshy fibres. All vessels and membranes which have any kind 

 of compression to execute are armed with these fibres. They are 

 always intimately connected with the nervous threads, but those 

 which belong to the purely vegetative functions contract, without 



