TOTAL QUANTITY OF BLOOD.' 687 



the area of nutritive and respiratory interchanges, is quite consistent 

 with the ascertained rapidity of the circulation, considered as a whole. 

 The circulation of the blood is said to be generally, but not always, 

 accelerated by an increased frequency of the heart's action. As life 

 advances, it becomes slower. 



Quantity of Blood in the Body. 



The total quantity of blood in the body has been the subject of 

 much investigation and discussion. The estimates of the older authors, 

 for the most part, were too high, whilst some of those of later writers 

 probably err in the opposite direction. The actual quantity in a man 

 of average height and weight has been supposed, by some, to be 26 or 

 30 Ibs., and by others only 12 Ibs. The ratio between the weight of 

 the blood and the weight of the body, the blood included, has been 

 estimated, by some authors, as 1 to 4f, and, by others, as 1 to 13 ; 

 according to these proportions, which differ so widely, the total quan- 

 tity of blood in the body of a man weighing 150 Ibs., would be either 

 upwards of 33 Ibs., or only about 11J Ibs. 



Observations on the quantity of blood lost in hemorrhages, are not 

 considered trustworthy, since in slow bleedings large quantities of fluid 

 are absorbed from the tissues, to refill the emptying vessels, and so 

 add largely to the amount of blood that may be drawn. The quantity 

 of blood escaping from the vessels in decapitated criminals, added to 

 that which may be subsequently expelled from the vessels, by cautious 

 injections of water, gives a more accurate result. But careful experi- 

 ments on animals are of most value. The method of Herbst, which 

 consists in quick bleeding from many vessels opened simultaneously, 

 gives the proportionate weight of the blood to that of the body, as from 

 1 to 12 in the ox, 1 to 16 in the dog, and 1 to 24 in the rabbit ; hence, 

 it would appear that the larger the animal, the greater is the proportion 

 of blood to the body. Valentin compared the specific gravity of the 

 blood drawn from a living animal, before, and after, the injection into 

 its bloodvessels of a given weight of water, the diminution of the spe- 

 cific gravity of the blood, by that quantity of water, serving as a factor 

 in the calculation; this method gives about 1 to 4J as the ratio to the 

 body in the dog. Chemical substances easy of detection, having been 

 injected into the blood, in known amojunts, and the quantity, in a cer- 

 tain portion of the blood drawn from the vessels, having been deter- 

 mined, data have been obtained for calculating the total quantity of 

 the blood ; this method shows a ratio of 1 to 8 or 9 (Blake). Welcker's 

 chromatic method is so called, because he estimates the amount of blood 

 left in the body after bleeding by means of the coloring matter. A 

 set of standard colored solutions is first prepared, by mixing a certain 

 known quantity of the blood of an animal with different known quan- 

 tities of water. The creature is then bled rapidly to death, and the 

 blood so drawn is weighed. The residual blood in the vessels, is then 

 estimated in the following manner: the vessels are washed out with 

 free injections of water; the whole body of the animal is likewise divided 

 into small pieces, and macerated, so as to extract all the cruorin in it; 



