416 OF NUTKITION. 



sidered as most independent and self-sustaining, the development is not only 

 checked by the want of a due supply of their appropriate materials, but it 

 is modified in a very remarkable degree by the presence of abnormal sub- 

 stances in the blood, which single out particular parts, and effect determinate 

 alterations in their nutrition, in such a constant manner as to show the 

 existence of a peculiar "elective affinity" between them. In so far, then, 

 as the process of Nutrition is dependent upon the due supply and normal 

 state of the Blood, its conditions have been already sufficiently discussed ; 

 and we have now only to consider it in its relations to the Tissues. 



331. The demand for Nutrition primarily arises from the tendency of the 

 organism to simple Increase or Growth. Of this we have the most character- 

 istic illustration in the multiplication of the first embryonic cell by the sim- 

 ple process of "duplicative subdivision ;" whereby a multitude of cells is 

 produced, every one of which is similar in all essential particulars to the 

 original. But after the different parts of this homogeneous embryonic mass 

 have taken upon themselves their respective modes of development, so as to 

 generate a diversity of tissues and organs, each one of these continues to 

 increase after its own plan; and thus the child becomes the adult, with com- 

 paratively little change but that of growth (chap, xviii, sect. 4). An ex- 

 cess of growth, taking place conformably to the normal plan of the tissue or 

 organ, constitutes Hypertrophy; whilst a diminution, without degeneration 

 or alteration of structure, is that which is properly distinguished as Atrophy. 



But Growth is not confined to the period of increase of the body gen- 

 erally ; for it may manifest itself in particular organs or tissues, as a normal 

 operation, at any subsequent part of life; as when an extraordinary demand 

 for the functional activity of a particular set of muscles is supplied by an 

 increase in the amount of their contractile tissue. And further, even where 

 there is no such manifestation of increase, there is really a continual growth 

 in all the tissues actively concerned in the vital operations, and this even to 

 the very end of life ; although it may be so far counterbalanced, or even 

 surpassed, by changes of an opposite kind, that instead of augmentation in 

 bulk, there is absolute diminution. 



332. The evolution of the complete organism from its germ, however, does 

 not consist in mere growth ; for by such a process nothing would be produced 

 but an enormous aggregation of simple cells, possessing little or no mutual 

 dependence, like tho.se which constitute the shapeless masses of the lowest 

 Algre. In addition to increase there must be Development, that is, a passage 

 to a higher condition, both of form and structure; so that the part in which 

 this change takes place becomes fitted for some special function, and is ad- 

 vanced towards the state in which it exists in the highest or most completed 

 form of its specific type. Thus the development of tissue consists in the 

 change from a simple mass of cells or fibres into any other form ; as in the 

 'production of Dentine from the cellular substance of the tooth-pulp, or in 

 the formation of Bone in the subperiostcal membrane. So, again, the de- 

 velopmental change is seen in the passage of an entire or gun from a lower 

 to a higher condition, by the evolution of new parts, or by a change in the 



tinctly traceable to a poison introduced through the blood, whose first influence is 

 exerted in modifying the physical and vital properties of that fluid; and the evidence 

 has been of late accumulating, that it is true also of the various forms of Cancer, the; 

 Ideal development of an abnormal structure being in this case also, nothing else than 

 the manifestation of the exigence of that peculiar matter in the blood, which is the 

 appropriate nutriment of its component tissues ; or, as Mr. Simon appropriately des- 

 ignates it, "a new excretory organ, which tends essentially to act> of eliminative 

 secretion, just us distinctly as the healthy liver or the healthy kidney." See Mr. 

 Simon's Lectures on General Pathology, pp 87, l- r >2 ; and Mr. Paget's Lectures on 

 Surgical Pathology, vol. i, p. 441, and vol. ii, pp. 528 ct scq. 



