MORBID FORMS OF NUTRITION. 705 



blood, by the quantity and quality of the food, by all the changes 

 which occur in the blood itself, by what is called the general condition 

 of the health, by exercise or the reverse, and by external conditions, 

 such as temperature, mechanical causes, pressure or violence, or chem- 

 ical agents. 



Nutrition is also affected, and modified, by the state of the nervous 

 system, as exemplified by the effect of emotions and other causes, 

 probably in the main through the action of the vasi-motor nerves reg- 

 ulating the diameter of the small arteries of a part. Perversions of 

 the condition of the nerves or nervous centres, may induce a perverted 

 state of the nutritive processes, both general and local. The forma- 

 tive and nutritive energy is, however, not derived from the nervous 

 system ; for it is manifested not only in animals destitute, so far as is 

 known, of any nervous system, but even in plants. Moreover, it begins 

 to act in the ovum, previous to the existence of a nervous system, which 

 system, indeed, is developed by its agency. Of the numerous instances 

 usually adduced to prove that the nervous system may directly guide, 

 or modify, the nutritive changes in the tissues, independently of its 

 action on the bloodvessels, none are satisfactory, if adduced in the case 

 of animals possessing bloodvessels ; for it is impossible, in such cases, 

 to exclude the action of the nerves upon these vessels. But there are 

 animals, low in the scale, such as the Beroe and other Coelenterata, in 

 which a nervous system exists, without bloodvessels; and, in these 

 cases, any action of the former, upon the nutritive processes, must be 

 direct, and not through the agency of vessels. The increased nutri- 

 tion or secretion from a part in such an animal, due to a stimulus 

 acting on its nerves, furnishes, unless this is influenced by the con- 

 traction of the tissues themselves, the requisite example of such direct 

 action. If so, by analogy, it might also occur in the vascular animals, 

 and in Man. 



Certain muscular organs, stimulated through the nerves, such as the 

 gravid uterus of the Mammalia, and the muscles of the frog after the 

 season of hibernation, undergo normal periodic enlargements. In 

 this form of over-nutrition, both the processes first mentioned usually 

 occur, viz., an increase in the size of the pre-existing elements, or 

 hypertrophy, and also an increase in their number, or hyperplasia. 

 Budge has actually observed this latter mode of increase, in the mus- 

 cles of the frog, new fibres being developed from nuclei arising from 

 the old ones within the sarcolemma of the pre-existing fibres. In such 

 cases, a corresponding increase takes place in the nerves, and new 

 nerve-fibres also appear to be developed by aid of the nuclei of the old 

 ones. (Kuhne.) The bloodvessels of such parts must also enlarge, a 

 change not due to simple dilatation, but to a coincident interstitial 

 hypertrophy of the tissue-elements of their walls. 



Various deviations from the normal standard of nutrition are met with in 

 the body ; they are fertile sources of organic disease, giving rise to the morbid 

 conditions known as hypertrophy and hyperplasia, neoplasia, atrophy, softening, 

 induration, degeneration, and inflammation, with its consequences. 



Hypertrophy and hyperplasia, already denned, are usually attributed, either 

 to an over-abundance of certain materials in the blood, suitable to the develop- 



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