458 OF NUTRITION. 



particular set of Muscles, which is subjected to frequent and energetic use, 

 acquires a great increase in bulk ; as we s6e in the arms of a Blacksmith or 

 Waterman, the legs of an Opera-dancer, &c. The hypertrophy of these 

 muscles is a consequence of their increased functional activity ; which, being 

 produced by an exertion of the will, and unaccompanied with any injurious 

 effects on the system, can scarcely be regarded as morbid. But there are 

 many instances in which the involuntary muscles acquire a greatly increased 

 strength, in consequence of an obstruction to their action, which results from 

 disease. Thus we see the right ventricle of the Heart become hypertrophied 

 (and dilated at the same time), where chronic pulmonary disease produces a 

 difficulty in the propulsion of the blood through the vessels of the lungs ; the 

 muscular fibres of the Bladder become enormously hypertrophied, when stric- 

 ture, diseased prostate, or other causes produce a demand for increased expul- 

 sive force on the part of that organ ; and those of the Stomach also become so, 

 in cases of stricture of the pylorus. As an instance of hypertrophy of a Se- 

 creting organ in consequence of an undue excitement of its function, we may 

 notice the enlargement which usually takes place in the Kidney, when its 

 fellow is incapacitated by disease. And the Nervous system presents us with 

 a very remarkable case of hypertrophy of a part, resulting from over-excite- 

 ment of its function ; for if young persons, who naturally show precocity of 

 intellect, are encouraged rather than checked in the use of their brain, the 

 increased nutrition of the organ (which grows faster than its bony case) occa- 

 sions pressure upon its vessels, it becomes indurated and inactive, and fatuity 

 and coma are the result. Local hypertrophy may be induced also by local 

 congestions ; but in such cases it will usually be found that the form of tissue 

 produced is of the lowest kind, unless the functional activity of the part be 

 increased by the congestion. Thus, when disease of the Heart produces 

 long-continued congestion of the Lungs, Liver, Spleen, &c., the bulk of 

 these organs increases ; but chiefly by the production of an additional amount 

 of interstitial Areolar tissue, which may result (as we .have seen) from the 

 simple consolidation of Fibrin ; and partly also (in the case of the spleen espe- 

 pecially) by the gorging of their distensible veins with blood. One of the 

 least explicable cases of Hypertrophy, is that which takes place in the Thyroid 

 gland, causing Bronchocele. So little is known of the normal office of this 

 organ, that it cannot be determined whether its increased size be due to an 

 increased activity of its functional operations, or to an unusual formative acti- 

 vity in its tissue, depending on some hidden cause. The connection of this 

 disorder with causes which affect the whole constitution rather than individual 

 parts, would seem to indicate the former. 



604. When the Waste of the Tissues is more rapid than their replacement 

 by Nutrition, Atrophy is said to take place ; and this may affect either the 

 whole body, or individual parts. General Atrophy, Marasmus, or emaciation, 

 may result from an insufficient supply of plastic matter, from want of forma- 

 tive power in the tissues themselves, or from their too rapid disintegration. 

 The insufficiency of the supply of nutritive matter may depend either on de- 

 ficiency in the azotized substances ingested as food, or on imperfect perform- 

 ance of those processes by which they are converted into the plastic element, 

 Fibrin. Hence, even when there is an ample supply of food, atrophy may 

 take place to a very severe extent, in consequence of disordered digestion, or of 

 want of vital power in the fibrin-elaborating cells. Again, we have reason to 

 believe that the formative power in the tissues themselves may be diminished, 

 so as to check the process of Nutrition, even when the plastic material is sup- 

 plied ; thus there seems to be a complete stoppage of this action in Fever, and 

 a diminution of it in that irritable state of the system which results from ex- 



