56 MATERIAL COMPOSITION OF MAN. 



times, it is dissolved ; at others, swims upon the fluid in brilliant plates, 

 or forms solid masses. It is obtained from biliary calculi by boiling in 

 water, and dissolving them afterwards in boiling alcohol. On cooling, 

 crystals of cholesterin separate. 



These inorganic and organic elements with others of less moment 

 discovered by modern chemists variously combined and modified by 

 the vital force, constitute the different parts of the animal fabric. 

 Chemistry, in its present improved condition, enables us to separate 

 them, and to investigate their properties ; but all the information we 

 derive from this source relates to bodies, that have been influenced by 

 the vital force, but are no longer so; and in the constant muta- 

 tions that occur in the system whilst life exists, and under its control- 

 ling agency, the same textures might exhibit very different chemical 

 characteristics, could our researches be directed to them under those 

 circumstances. Whenever, therefore, the physiologist has to apply 

 chemical elucidations to operations of the living machine, he must re- 

 collect, that all his analogies are drawn from dead matter, which dif- 

 fers so widely from the living as to suggest the necessity of a wise and 

 discriminating caution. 



The components of the animal body are invariably found under two 

 forms solids and fluids. Both are met with in every animal, the for- 

 mer being derived from the latter; for, from the blood every part of 

 the body is separated; yet they are mutually dependent, for every 

 liquid is contained in a solid. The blood itself circulates in solid 

 vessels. Both, too, possess an analogous composition ; are in constant 

 motion, and incessantly converted from one into the other. Every 

 animal consists of a union of the two ; and this union is indispensable 

 to life. Yet certain vague notions with regard to their relative pre- 

 ponderance in the economy, and to their agency in the production of 

 disease, have led to discordant doctrines of pathology, the solidists 

 believing, that the cause of most affections is resident in the solids ; 

 the humorists, that we are to look for it in the fluids. In this, as in 

 similar cases, the mean will lead to the most satisfactory result. The 

 causes of disease ought not to be sought in the one or the other exclu- 

 sively. 



c. Of the Solid Parts of the Human Body. 



A solid is a body whose particles adhere to each other, so that they 

 do not separate by their own weight ; but require the agency of some 

 extraneous force to effect the disjunction. Anatomists reduce all the 

 solids of the human body to twelve varieties ; bone, cartilage, muscle, 

 ligament, vessel, nerve, ganglion, follicle, gland, membrane, areolar 

 membrane, and viscus. 



1. Bone is the hardest of the solids. It forms the skeleton ; the 

 levers for the various muscles to act upon ; and serves for the protec- 

 tion of important organs. 



2. Cartilage is of a white colour, formed of very elastic tissue; 

 covering the articular extremities of bone to facilitate their movements ; 

 sometimes added to bones to prolong them, as in the case of the ribs; 



