546 OF NUTRITION. 



attributed solely to the latter ; the previous preparation of their bodies for the 

 reception and development of the zymotic poison, being altogether overlooked. 

 It is impossible, however, for any one who carefully examines the evidence, to 

 hesitate for a moment in the conclusion, that the fatality of epidemics is almost 

 invariably in precise proportion to the degree in which an impure atmosphere 

 has been habitually respired ; that an atmosphere loaded with putrescent mias- 

 mata may afford a nidus wherein a zymotic poison undergoes a marked increase 

 in quantity and intensity, the putrescent exhalations from the lungs and skin 

 of the living subject being at least as effectual in furnishing such a " nidus," as 

 are the emanations from fecal discharges or from other decomposing matters ; 

 that the habitual respiration of such an atmosphere tends to induce a condition 

 of the blood, which renders it peculiarly susceptible of perversion by the intro- 

 duction of zymotic poisons, and which favors their multiplication within the 

 system j 1 and lastly, that by due attention to the various means of promoting 

 atmospheric purity, and especially to efficient ventilation and sewerage, the rate 

 of mortality may be enormously decreased, the amount and severity of sickness 

 lowered in at least an equal proportion, and the fatality of epidemics almost 

 completely annihilated. And it cannot be too strongly borne in mind, that 

 the efficacy of such preventive measures has been most fully substantiated, in 

 regard to many of the very diseases in which the curative power of Medical 

 treatment has seemed most doubtful ; as, for example, in Cholera and Malignant 

 Fevers. 



CHAPTER XI. 



OF NUTRITION. 



1. General Considerations. Formative Power of Individual Parts. 



585. THE function of Nutrition, considered in the widest acceptation of the 

 term, includes the whole series of operations, by which the alimentary materials 

 prepared by the Digestive process, introduced into the system by Absorption, 

 and carried into its penetralia by the Circulation are converted into Organized 

 tissue ; but in a more limited sense it may be understood as referring to the last 

 of these operations only, that of Histogenesis or tissue-formation, to which all 

 the other organic functions, in so far as they are concerned in maintaining the 

 life of the individual, are subservient, by preparing and keeping in the requisite 

 state of purity the materials at the expense of which it takes place. It has been 

 shown in the earlier portion of this volume, that every integral part of the living 

 body possesses a certain capacity for growth and development, in virtue of which 

 it passes through a series of successive phases, under the influence of the steady 

 heat, which in the warm-blooded animal is constantly acting upon it (CHAP, in., 

 SECT. 1, 2) ; this capacity being an endowment which it derives by direct descent 



1 A careful consideration of the very satisfactory evidence which has been of late yeai\s 

 collected on this point, must (in the Author's opinion) satisfy any competent and unprejudiced 

 inquirer, that Endemic Fevers, originating in local causes (marsh miasmata and the like), 

 and affecting those only who are exposed to such causes, may find, by the crowding together 

 of infected subjects, a nidus for development within the Human system ; so that these dis- 

 eases then become communicable by human intercourse, although not so originally. For 

 a discussion of this subject, see the Articles on "Yellow fever" in the "Brit, and For. 

 Med.-Chir. Rev.," vols. i. and iv. 



