ITS PHYSICAL, CHEMICAL, AND STRUCTURAL CHARACTERS. 233 



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



171. 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 consiste'uce and density somewhat greater than that of water, but espe- 

 cially 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 approach- 

 ing to black, when it is drawn from a vein. This difference of color, how- 

 ever, 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 effected, as in the foetus, and it may be 

 especially noticed during operations performed under the influence of anaes- 

 thetic agents ; it has also been remarked by Dr. John Davy, as usually char- 

 acterizing the arterial blood of the inhabitants of hot climates, 1 and it occurs 

 in blood that has been allowed to stagnate either in arteries or veins ; 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. 

 It is well marked in the blood returning from an actively secreting gland, 

 and from a quiescent muscle. 2 When ordinary venous blood is examined in 

 thin layers, it presents a deep red or purple tint by reflected light, but by 

 transmitted light it assumes a greenish hue, thus presenting the phenomena 

 of Dichroisrn ; a peculiarity which is not possessed by arterial blood ( Brucke) ; 

 but when the gases of the blood are wholly removed by exhaustion, both 

 arterial and venous blood assume a deep black color. 3 The specific, gravity 

 of the Blood is stated by Nasse 4 to vary (within the limits of health) between 

 1050 and 1059 ; the average being taken at 1055. The specific gravity of 

 of the Corpuscles is about 1088, and that of the fluid in which they float 

 about 1028. The chemical reaction of the blood is invariably alkaline, and 

 very important purposes are served by this alkalinity. The temperature of 

 the Blood, usually considered to be about 100 F., has been found by Ber- 

 nard, 5 in an extensive series of observations made with extremely sensitive 

 thermometers, to vary several degrees in different parts of the body. The 



f. Anat. und Phys., Bd. iii, p. 281). Blake's method consisted in the injection of a 

 definite quantity of some saline compound, as sulphate of alumina, and its subse- 

 quent quantitative determination, in a portion of blood drawn from another part of 

 the system. This means of estimation gives the proportion of blood to that of the 

 body" as 1 : 8 or as 1 : 9 (see Prof. Dunglison's Physiol., 8th edit., vol. 1, p. 3-37), and 

 is in accordance with the results obtained by Lehmann and Weber in their examina- 

 tions of the quantity of blood discharged from two decapitated criminals (Lehmann, 

 Lehrbuch, 2d edit , Bd. ii, p. 234). For recent papers on this subject, which, how- 

 ever, add little to our knowledge, see Brozeit, Pfliiger's Archiv, 1870, p. 353; Stein- 

 berg in idem, 1873, p. 101 ; and Gscheidlen, in idem, 1873, p. 350. Brozeit obtains 

 the^Hsematin by means of ether and hydrochloric acid from a given quantity of the 

 washings after venesection, compares it with that in the same quantity of blood, and 

 makes the requisite calculation. Steinberg proceeds on the principle that solutions 

 of haemoglobin, when of a certain strength, transmit green light. 



1 Anatomical and Physiological Researches, vol. ii, p. 14@. This fact, which har- 

 monizes with the inference to be drawn from the observed results of a high external 

 temperature in reducing the excretion of carbonic acid (chap, ix), is of great prac- 

 tical importance. 



2 Bernard, Le9ons, 1859, vol. i, p. 324. 



3 Setschenow, Sitszungsberichte d. Kais. Akad d. Wiss., xxxvi, 1859. 



Wagner's Handworterbuch der Phys., Art. Blut, Bd. i, p. 82. 

 Le9ons sur les Liquides de 1'Organisme, 1859, iii, iv, v, vi. 



16 



