FORMATIVE POWER OF INDIVIDUAL PARTS. 415 



CHAPTER X. 



OF NUTRITION. 



1. General Considerations. Formative Power of Individual Parts. 



330. THE function of Nutrition, considered in the widest acceptation of 

 the term, includes that whole series of operations by which the alimentary 

 materials prepared by the Digestive process, introduced into the system by 

 Absorption, and carried into its penetralia by the Circulation are converted 

 into Organized tissue ; but in a more limited sense it may be understood as 

 referring to the last of these operations only, that of Histogenesis or tissue- 

 formation, to which all the other organic functions, in so far as they are con- 

 cerned in maintaining the life of the individual, are subservient, by preparing 

 and keeping in the requisite state of purity the materials at the expense of 

 which it takes place. Every integral part of the living body possesses a 

 certain capacity for growth and development, in virtue of which it passes 

 through a series of successive phases, under the influence of the steady Heat, 

 which in the warm-blooded animal is constantly acting upon it ; this capac- 

 ity being an endowment which it derives by direct descent from the original 

 germ (chap, i), but undergoing a gradual diminution with the advance of 

 life (chap, xx), until the power of maintenance is no longer adequate to an- 

 tagonize the forces that tend to the disintegration of the system. It has been 

 also shown (chap, vii), that notwithstanding the diversities in the structure 

 and composition of the several tissues, the Blood supplies the materials which 

 each requires ; every tissue possessing (so to speak) an elective affinity for 

 some particular constituents of that fluid, in virtue of which it abstracts them 

 from it, and appropriates them to its own uses. But it has been shown, on the 

 other hand, that the " formative capacity" does not exist in the tissues alone, 

 but is shared by the Blood, which must itself be regarded as deriving it from 

 the original germ ; for there are certain simple kinds of tissue, which appear 

 to take their origin directly in its plastic components. Of others, which 

 cannot be said thus to originate in the blood, the development seems to be 

 entirely determined by the quantity of their special pabula which it may 

 contain. Thus, an increase of Adipose tissue takes place, when the blood 

 habitually includes an unusual amount of fat; an augmentation in the pro- 

 portion of the Red Corpuscles of the blood may be distinctly observed (espe- 

 cially if it has been previously diminished unduly), when an additional sup- 

 ply of iron is afforded ; and when one of the Kidneys has been removed, or 

 is prevented by disease from performing its normal function, the other, if it 

 remain healthy, undergoes an extraordinary increase in size, so as to per- 

 form the duty of both organs, the augmented development of its secreting 

 structure being here also fairly attributable to the accumulation of its ap- 

 propriate materials in the blood. 1 Even of those tissues which must be coii- 



1 This principle is one most fertile in Pathological applications; for there can be 

 little doubt that the development of many morbid growths is due, not so much to a 

 perverted local action, as to the presence of certain morhid matters in the blood, 

 which determines the formation of tissues that use them as their appropriate pabulum. 

 Such is pretty obviously the case with those disorders, which (like the Exanthemata) 

 are universally admitted to be of "constitutional" character, and which are dis- 



