156 OF THE BLOOD. 



32 Ibs. of blood, and a woman weighing 127 Ibs. would have 27 Ibs. of blood. 

 It can scarcely be doubted that this statement is too high ; and it is not difficult 

 to discern an important fallacy in the method on which it was based. For, how- 

 ever rapidly the operation may be performed, some portion of the water injected 

 will transude from the vessels into the surrounding tissues, and will escape by 

 the kidneys; and thus, the degree of its dilution being diminished, the estimate 

 of the total amount of the blood will be raised considerably above the reality. 

 It has been more recently proposed by more than one experimenter to inject, in 

 place of water, some saline compound, whose presence in the blood might easily 

 be determined quantitatively, and which should neither be so poisonous as to 

 produce speedy death, nor be capable of such rapid transudation as to escape too 

 readily into the tissues or the urine. The sulphate of alumina has been employed 

 for this purpose by Prof. Blake 1 (of St. Louis, U. S.) ; and his experiments lead 

 to the conclusion that the proportion of blood in the body of a Dog is as 1 : 8 or 

 1:9; so that, applying the same proportion to Man, the quantity of blood in a 

 Human body weighing 144 Ibs. would be 16 or 18 Ibs. Several circumstances 

 lead to the belief that this estimate is not far from the truth ; but it cannot be 

 doubted that a considerable variation in the relative amount of blood will exist 

 among different individuals. 



2. Physical, Chemical, and Structural Characters of the Blood. 



137. The Blood, as it flows forth from an opening in a large vessel, is an 

 apparently homogeneous liquid, possessing a slight degree of viscidity, with a 

 consistence and density somewhat greater than those of water, but especially 

 distinguished by its color, which is usually of a bright scarlet when it is drawn 

 from an artery, and of a dark purple, sometimes almost approaching to black, 

 when it is drawn from a vein. This difference of color, however, is by no means 

 constant; for arterial blood may sometimes be unusually dark, whilst venous 

 blood is occasionally so florid that it might almost be taken for arterial. The 

 former condition is observable, when from any cause the respiratory process is 

 imperfectly performed, and may be especially noticed during operations per- 

 formed under the influence of anaesthetic agents ; it has also been remarked by 

 Dr. John Davy, as usually characterizing the arterial blood of the inhabitants 

 of hot climates f but, in any of these cases, the ordinary arterial hue is acquired 

 by the blood when it has been sufficiently exposed to the air. The florid hue is 

 presented by the venous blood of animals which are made to respire pure oxygen; 

 but it seems normal with some individuals whose respiration is peculiarly active. 

 The specific gravity of the Blood is stated by Nasse, 3 as the result of numerous 

 observations, to vary (within the limits of health) between 1050 and 1059 ; the 

 average being taken as 1055. The principal source of this variation is the want 

 of constancy in the proportion of the red corpuscles in the blood ; for the specific 

 gravity of these, when separately examined, is found to be as high as 1088.5, 

 whilst that of the liquid in which they float is no more than 1028; and hence the 

 specific gravity of the blood of men is usually higher than that of women ( 159), 

 and that of the portion of blood first drawn exceeds that of the portion which 

 flows last ( 162). The chemical reaction of the Blood seems to be invariably 

 alkaline; and very important purposes are served by this alkalinity ( 83, 84). 

 When we add that the Blood has a saltish taste, and a faint odor resembling 

 that of the pulmonary and cutaneous exhalations of the animal from which it is 



1 See Prof. Dunglison's " Human Physiology," seventh edit. vol. ii. p. 102. 



2 "Anatomical and Physiological Researches," vol. ii. p. 140. 



3 Wagner's "Handworterbuch der Physiologic," " Blut" bandi. p. 82. 



