ELEMENTARY PARTS OF ANIMAL STRUCTURES. 105 



CHAPTER III. 



OF THE ELEMENTARY PARTS OF ANIMAL STRUCTURES. 



162. IN the investigation of the operations of a complex piece of Me- 

 chanism, and in the study of the forces which combine to produce the 

 general result, experience shows the advantage of first examining the 

 component parts of the Machine, its springs, wheels, levers, cords, 

 pulleys, &c., determining the properties of their materials, and ascer- 

 taining their individual actions. When these have been completely 

 mastered, the attention may be directed to their combined actions : and 

 the bearing of these combinations upon each other, so as to produce the 

 general result, would be the last object of study. 



163. This seems the plan which the Student of Physiology may most 

 advantageously pursue, in the difficult task of making himself acquainted 

 with the operations of the living Organism, and with the mode in which 

 they concur in the maintenance of Life. He should first examine the 

 properties of the component materials of the structure, in their simplest 

 form : these he will find in its nutrient fluids. He may next proceed to 

 the simplest forms of organized tissue, which result from the mere solidi- 

 fication of those materials, and whose properties are chiefly of a mechani- 

 cal nature. From these he will pass to the consideration of the struc- 

 ture and actions of those tissues that consist chiefly of cells ; and will 

 investigate the share they take in the strictly vital operations of the 

 economy. Next his attention will be engaged by the tissues produced 

 by the transformation of cells ; of which some are destined chiefly for 

 affording mechanical support to the fabric, and others for peculiar vital 

 operations. And he will be ttyen prepared to understand the part which 

 these elementary tissues severally perform in the more complex organs. 

 A due knowledge of these elementary parts, and of their physical, chemi- 

 cal, and vital properties, is essential to every one who aims at a scientific 

 knowledge of Physiology. True it is, that we may study the results of 

 their operations, without acquaintance with them ; but we, should know 

 nothing more of the working of the machine, than we should know of 

 a cotton-mill, into which we saw cotton-wool entering, and from which 

 we saw woven fabrics issuing forth ; or of a paper-making-machine, which 

 we saw fed at one end with rags, and discharging hot-pressed paper, cut 

 into sheets, at the other. The study of these results affords, of course, 

 a very important part of the knowledge we have to acquire respecting 

 the operations of the machine ; but we could learn from them very little 

 of the nature of the separate processes effected by it; still less should 

 we be prepared, by any disorder or irregularity in the general results, to 

 seek for, and rectify, the cause of that disturbance in the working of the 

 machine, by which the abnormal result was occasioned. 



164. Now just as in a cotton-mill, there are machines of several 

 different kinds, adapted to effect different steps of the process by which 

 the raw material is converted into the woven fabric, so do we find that 

 in the complex Animal fabric there is a great variety of organs for per- 



