554 OP NUTRITION. 



ment are being normally carried on, such absorption may be considered to be 

 impossible. On the other hand, if a part die en masse, it is not removed by 

 absorption, but becomes isolated by the separation and recedence of the living 

 parts, and is then cast out altogether, even from the interior of the body as we 

 see in the case of a necrosed bone ; its condition being then essentially the same 

 as that of the outer layers of the tegumentary organs, which are cut off, by their 

 distance from a vascular surface, from all further nutrient change. The differ- 

 ence between these two modes of removal is well seen (as Mr. Paget has re- 

 marked) in the case of the Teeth ; for the fangs of the deciduous teeth undergo 

 degeneration, when the current of nutrition is diverted towards those which are 

 to succeed them, their materials being slowly decomposed so as to become soluble, 

 and being gradually removed by absorption, so that nothing is left at last but 

 the crowns of the teeth ; on the other hand, the permanent teeth which are not 

 to be succeeded by others, when no longer receiving their due nutrition, die, and 

 are cast out entire. 



594. Among the conditions of healthy Nutrition, a due supply of Nervous 

 power is commonly enumerated ; and it cannot be questioned that the want of 

 such a supply is frequently the source of a perversion of the normal operations. 

 This, however, by no means proves that the formative power is derived from 

 the nervous system ; and such an idea is at once negatived by a number of in- 

 contestable facts. Yet it may be freely admitted that the right direction and 

 application of this power in Nutrition may sometimes depend upon guidance 

 and direction afforded by the Nervous centres, in the same manner as the Secret- 

 ing process is capable of being thus influenced ; in fact, we can scarcely explain 

 in any other mode that influence of mental states upon the nutrient operations, 

 which frequently leads to very important modifications of them. The whole 

 of this subject, however, will be more appropriately considered hereafter (CHAP. 

 XVII.). 1 



2. Varying Activity of the Nutritive Processes. Reparative Operations. 



595. Without any change in the character of the Nutritive processes, there 

 may be considerable variations in their degree of activity ; and this, either as 

 regards the entire organism, or individual parts, though most commonly the 

 latter. These variations may be so considerable as to constitute Disease ; 

 though there are some which take place as part of the regular series of Physio- 

 logical phenomena. Thus, as we have seen, it is to the excess of formative 

 activity, that the increase of the organism in the earlier period of life is due, its 

 " waste" being at the same time extremely rapid ; whilst it is to a correspond- 

 ing reduction in the regenerative power, and not to positive excess of "waste" 

 or decay (this, indeed, taking place very slowly), that the gradual decline of 

 the organism in advancing years is to be attributed. So also we find that local 

 as well as general variations may take place, as a part of the regular series of 

 vital phenomena ; and this during the period of adult life, as well as in the 

 earlier and later epochs. Thus all those differences in the proportional develop- 

 ment of the several parts of the organism, which mark the distinction between 

 the adult and the child, even where (as in the case of a dwarf), there is no dif- 

 ference in stature, result from a decline in the formative capacity of those which 

 are peculiarly adapted to the wants of the earlier stage (the Thymus gland, for 

 example), and from an increased activity of nutrition in tnose which are destined 

 to the use of the adult, the Generative organs more particularly. And the 



1 In the treatment of this subject, the Author has made free use of the valuable materials 

 contained in Mr. Paget's "Lectures on Nutrition, Hypertrophy, and Atrophy" ("Med. 

 Gaz.," 1847), which have enabled him, whilst still expressing the same general doctrines as 

 in previous editions, to make great improvements in the exposition and illustration of them. 



