714 SPECIAL PHYSIOLOGY. 



destructive of their substance. So essential is oxygen for this pur- 

 pose, that the deprivation of it, for but a few minutes, is fatal to the 

 life of these two tissues. As to the carbonic acid gas of the blood, not 

 only is it neither nutrient nor stimulant, but it is the chief ultimate 

 product of the oxidation of the tissues, being probably derived, how- 

 ever, from the oxidation of intermediate compounds, into which the 

 materials of the used-up blood and tissues break down. It is the ulti- 

 mate eifete form in which most of the decomposed carbonaceous sub- 

 stances are eliminated from the body. It is an impurity in the blood, 

 which requires to be incessantly expelled from it, and, indeed, is so 

 displaced by the aid of the oxygen in respiration. Under its influence, 

 the scarlet color and the other properties of arterial blood are changed, 

 and the blood becomes dark and venous. It is so detrimental to the 

 life of both the nervous and muscular tissues, that, in cases of as- 

 phyxia, in which it ceases to be eliminated by the lungs, death seems 

 rather to take place from the poisonous nature of the accumulated 

 carbonic acid, than from the mere absence of the nutritive, or stimu- 

 lating and vivifying, oxygen. 



The nutritive properties of the blood differ according to many cir- 

 cumstances, being influenced by the character of that fluid, the age, 

 sex, temperament, habits as to exercise and occupation, the constitu- 

 tional state, and the nature of the food. Thus arterial blood is more 

 nutritive and stimulating than venous blood, which will not long sup- 

 port life, especially that of the nervo-muscular apparatus. Arterial 

 blood not only contains more oxygen, and less carbonic acid, but its 

 liquor sanguinis is richer in fibrin, and its corpuscles contain more 

 cruorin and saline substances, and much less fat their total solid 

 matter being less than that of the corpuscles in venous blood. The 

 fluid part of arterial blood also contains less fat, but more saccharine 

 and extractive matters. Again, the blood is less rich in childhood 

 than before birth ; its corpuscles increase, however, at puberty, but, 

 after fifty years of age, again diminish. The blood is richer in solid 

 contents, especially in red corpuscles, in men than in women ; the 

 same is true of plethoric and sanguine persons, as compared with those 

 of lymphatic or serous constitution. The quantity of the fatty matter 

 is more influenced by the diet, than that of the other organic proxi- 

 mate constituents. Exercise in the open air purifies and oxygenates 

 the blood. This fluid is, of course, profoundly modified in disease. 



Hemorrhage or Loss of Blood. 



The escape of blood from its vessels into the surrounding tissues is 

 named extravasation; if into one of the cavities of the body, or exter- 

 nally, it is named hemorrhage. The loss of from four to six pounds 

 of blood, from one or more of the great vessels, will generally prove 

 fatal to an adult; but if the hemorrhage be slower, much larger quan- 

 tities may be drawn from the bloodvessels, without a directly fatal 

 issue. Death from sudden hemorrhage is caused by the want of suf- 

 ficient blood to supply the nervous centres, so that fatal syncope, i. e., 

 fainting, takes place; when death occurs from prolonged hemorrhage, 



