USE OF THE BLOOD IN NUTRITION. 707 



part of the surface of a tissue or organ, causing a loss of substance, or sore 

 known as an ulcer. Gangrene or mortification, is the complete molar death of 

 a part, dependent, sometimes, on excessive inflammation, causing obstruction 

 or occlusion of the larger or smaller bloodvessels, or an actual destruction by 

 violence, heat, cold, or chemical agents. The body may also be wounded, or 

 parts even completely detached from it. 



As inflammation and its consequences are essentially derangements of the 

 nutritive process, so, on the other hand, all the reparative phenomena seen in 

 the living animal body, which tend to preserve life, consist in most remarkable 

 and energetic manifestations of modified development, growth, and nutrition. 

 Thus, the cavity of an abscess is chiefly closed by the collapse of its sides ; 

 but, also, by a. new and very vascular, soft, red formation, in its interior, 

 known as granulations, which are developed from new cell-elements, partly 

 metamorphosed into connective tissue, and partly into bloodvessels, whilst 

 certain of the cells escape as pus ; ultimately, these granulations cohere, and 

 the orifice being closed up, is covered by new epidermis, or by cicatrization. An 

 ulcer, or a wound is filled up, and healed, in a similar manner, by granula- 

 tion, suppuration, and cicatrization, the resulting mark being named a scar, 

 or cicatrix. The temporary covering or natural dressing of an ulcer, known 

 as a scab, consists of dried exuded materials and pus. Gangrenous parts are 

 detached, separated, and thrown off, by a remarkable ulcerative process, or 

 molecular decay, occurring, not in the dead parts, but in the living parts in 

 immediate proximity to them ; when these are detached, the raw surface is 

 healed by granulation, suppuration, and cicatrization. 



The healing of actual wounds differs according to the extent, depth, and rel- 

 ative proximity of the surfaces, and the degree of their exposure to the air. 

 It may sometimes occur by immediate or direct union, as in the healing of sub- 

 cutaneous wounds, without any manifest inflammation, and, it is said, even 

 without any observable exudation of intermediate or uniting plastic matter. 

 Sometimes this may also occur in the healing of external cut surfaces, which 

 have quite ceased to bleed, and can be maintained in accurate and immovable 

 apposition, and from between which air can be totally excluded. Most fre- 

 quently, however, healing is accompanied by more or less inflammatory action 

 and the formation of a. new uniting substance; this constitutes union by adhe- 

 sive inflammation, or by the first intention. In this mode of union, plastic mat- 

 ter is exuded, new cells are formed and converted into connective and capil- 

 lary tissue, and so the divided, but apposed surfaces, are joined. When the 

 wound is deep, or the loss of substance is great, or the apposition of the sur- 

 faces impossible, or when, from any other cause, the adhesive inflammation 

 does not happen, then the surfaces granulate and suppurate like those of an 

 ulcer or abscess, and when these have closed up the cavity, cicatrization ensues. 

 The extent and mode of reparation in each .tissue, and in various animals, 

 will be explained in the Section on Development. In all cicatrices, or other 

 repaired parts, nutritive changes afterwards go on, resulting, as in the healthy 

 tissues, in the maintenance of the form and characters of the newly developed 

 tissue or scar. 



Offices of the Blood and of its Several Constituents in Nutrition. 



The general fact, already indicated, that the blood is the source of 

 all the nutrient material for the solid tissues of the body, is iHustrated 

 in many ways. Thus, the activity of the nutritive process is coinci- 

 dent with the quantity and quality of the blood supplied to a particular 

 part or organ. Unless it be constantly supplied, through the absorbent 

 system, with fresh nutriment from food, it becomes itself impoverished, 

 showing the demand made upon it by the nutritive wants of the solid 

 tissues. Ligature of the arteries of a part is followed by a diminution 

 in its size, owing to defective nutrition ; and not only does complete 

 closure of the arteries accomplish this, but even their compression. 



