708 SPECIAL PHYSIOLOGY. 



There are instances in which an increased supply of blood, through 

 enlargement of the arteries, occurs as a natural phenomenon in the 

 living body, and, in such cases, this determination of blood, as it is 

 called, is accompanied by an increased growth in the part or organ 

 supplied, as exemplified in the annual development of the antlers of 

 the stag, and in the periodic enlargement of the mammary glands in the 

 Mammalia, for the supply of their young with milk. Again, the fall- 

 ing of the antlers, and the disappearance of portions of healthy bone, 

 in the ordinary nutrition of that texture, are always preceded or 

 accompanied by a gradual shrinking and final closure of the vessels 

 which nourish them, by the filling up of the Haversian canals of the 

 bony tissue ; thus nutrition is arrested, as the supply of blood is cut 

 off. Lastly, hemorrhages or bleedings are followed, eventually, by 

 diminished nutrition of the body. But the immediate effects of severe 

 hemorrhage are most remarkable. The functional activity of the mus- 

 cular and nervous systems, the exercise of which also demands rapid 

 nutritive changes, is either enfeebled, suspended, or lost. Every sen- 

 sation, perception, emotion, or volition, and every movement, is 

 accompanied by disintegration of nervous or muscular tissue, or of 

 both ; these tissues are maintained in a fit state for action, by a due 

 supply of oxygenated blood and nutritive plasma, and the several 

 changes which occur in them and in the blood, are retrogressive chemi- 

 cal decompositions, accomplished through the agency of the oxygen 

 conveyed in the latter. Accordingly, a loss of blood from hemor- 

 rhage, a diminution of that fluid from pressure on the vessels, or an 

 arrest of the circulation from ligature, or other causes, is followed by 

 a diminution, suspension, or annihilation of the functions of a muscle 

 or nervous centre. Similar results ensue from serious alterations in 

 the quality of the blood, as when the proportion of oxygen in it is 

 deficient, or when carbonic acid is in excess, as is seen in the imme- 

 diate loss of consciousness and muscular power, which follows the arrest 

 of the decarbonizing and oxygenating processes of respiration. The 

 nutrition of the body, generally, also becomes defective, from a con- 

 tinually diminished supply of pure air, owing to the blood not being 

 then duly oxygenated and purified. Finally, the influence of the blood 

 in stimulating and nourishing the tissues, is directly proved by the 

 remarkable resuscitating effects of injecting that fluid into the veins of 

 persons or animals, previously deprived of blood by accidental or 

 intentional hemorrhage, the powers of the whole system which have 

 previously been suspended, being, in this way, almost instantaneously 

 restored. 



The nutritive, stimulating, and resuscitating powers of the blood, 

 depend on the chemical constitution of the liquor sanguinis, and on 

 the number, composition, and properties of the corpuscles which it 

 contains ; and the special offices of the different parts of this fluid, for 

 the processes of nutrition, may be referred both to its morphological 

 and chemical constituents, which have already been described (pp. 

 57, 79). 



The white corpuscles appear to serve, at all periods after birth, for 

 the renovation of the red or colored ones. They are very abundant 



