INTRODUCTION. 29 



body in one consistent form, and within certain pre- 

 scribed limits. 



When condensed into a firm and compact struc- 

 ture it constitutes the various membranes of the 

 body, which are more or less extensive. These 

 drawn into a cylindrical shape from the various 

 tubes called vessels, which, under more or fewer 

 ramifications, are diffused over the whole corporeal 

 system. The filaments termed fibres are also com- 

 posed of the cellular substance, and the bones them- 

 selves are nothing but modifications of the same 

 substance, indurated by the accumulation of terrene 

 particles. 



Cellular substance is ascribed by chemists to that 

 peculiar modification of animal matter termed gela- 

 tine. It is entirely soluble in boiling water, and the 

 solution assumes, when cold, the appearance of jelly. 



Of the medullary matter, or, as it is sometimes 

 termed, the cerebral substance, we have as yet been 

 unable to discern the more minute organization. 

 To the eye it presents the appearance of a soft and 

 whitish matter, where nothing is distinguishable ex- 

 cept a number of infinitely small globules. It is not 

 itself susceptible of apparent motion, yet is it in 

 it that the astonishing power resides of transmitting 

 to the mind the impressions of the senses, and of 

 communicating to the muscles the impulses of the 

 will. The brain is, in a great measure, composed of 

 this medullary substance, and the spinal marrow and 

 nerves, which are distributed through all the sen- 

 sitive parts of the frame, are, as far as their essence 



