346 OF NUTRITION. 



rarely take place in these tissues without an especial stimulus of this 

 kind. Thus we find that, when a larger supply of nutritive matter is 

 introduced into the circulation, than is required to repair the waste of 

 these tissues, they do not undergo an increased development in conse- 

 quence ; but an augmented nutrition, is produced, either in the adipose 

 tissue, or in the glandular structures by which the superfluous matter is 

 eliminated from the system. 



618. Augmented nutrition, or Hypertrophy, then, may result in cer- 

 tain organs, from an excessive supply of their nutrient materials ; as in 

 the case of the kidney, just mentioned ; or as in the enlargement which 

 we not unfrequently meet with in the livers of those, who have resided 

 long in warm climates, and who have not sufficiently restricted their 

 supply of non-azotized food to the small amount required for respiration 

 at an elevated temperature, thereby sending an over-supply of that par- 

 ticular class of bodies, to be separated from the blood by the liver. 

 Or, in other cases, the increase of functional activity may be the imme- 

 diate cause of the increased nutrition ; and this we see, not only in the 

 nervous centres and voluntary muscles, which are put in action by the 

 will, but in parts over which the mind has no control. Thus the heart 

 becomes hypertrophied, when an obstruction exists in the pulmonary or 

 systemic circulation, to overcome which, increased energy of contraction 

 is required ; and in the same manner the muscular coats of the urinary 

 and gall-bladder acquire an extraordinary increase of thickness, when 

 long-continued obstruction, by calculi or stricture in the canals issuing 

 from them, impedes the free -exit of their contents. Sometimes, how- 

 ever, a local hypertrophy takes place, which cannot be accounted for in 

 either of these modes ; as when a single finger is enlarged out of all 

 proportion to the rest, or the whole of one hand increases to a much 

 greater size than the other, by the existence (as it would seem) in the 

 individual part of that tendency to unusual development, which, when it 

 aifects the whole body uniformly, produces a gigantic stature. 



619. Now a precisely reversed series of conditions diminishes the 

 activity of the nutrient processes, and induces a state of Atrophy. 

 If there be a deficiency in the general amount of nutriment introduced 

 into the system by absorption, a general atrophy results ; and the waste 

 being more rapid than the supply, there is a diminution in the volume 

 of all the tissues excepting the nervous, which seems to have its nutri- 

 tion kept up even to the last, at the expense of all the rest. Such a 

 condition results not merely from the want of food, but also from the 

 want of power to assimilate it ; and thus emaciation may take place 

 to an excessive degree, when food of the most nutritive character is 

 copiously supplied, and when the appetite for it is vehement ; in conse- 

 quence of disorder in the mesenteric glands, or in some other part of 

 the apparatus particularly concerned in the elaboration of fibrine. A 

 partial atrophy may result, in like manner, from a deficiency of the 

 materials required for the formation of an individual tissue or organ ; 

 thus the adipose tissue throughout the body, may be atrophied, in con- 

 sequence of an absence of those materials in the food, which are capable 

 of being converted into fatty matter. Or a particular organ may be 

 atrophied, by a diminution of the circulating current that should flow 



