384 BLOOD AND LYMPH. 



1.055. The most satisfactory method of determining this factor is, 

 of course, to compare the weight of a known volume of blood with 

 that of an equal volume of water, but for observations upon human 

 beings such small quantities of blood must be used that recourse must 

 be had usually to a more indirect method. Perhaps the simplest of 

 the methods suggested is that devised by Hammerschlag.* In this 

 method a mixture is made of chloroform (sp. gr., 1.526) and benzol 

 (sp. gr., 0.889). The mixture is made in such proportions as to 

 have a specific gravity of about 1.055. A drop of blood from the 

 finger is shaken into this mixture; if the drop sinks to the bottom 

 it is evident that the specific gravity of the blood is higher than that 

 of the mixture, and the reverse is true if the drop rises. By adding 

 more of the chloroform or of the benzol, as the case may be, the 

 specific gravity of the mixture may be quickly altered so as to be 

 equal to that of 'the drop of blood, which will then float in the liquid 

 without a distinct tendency to rise or fall. The specific gravity of 

 the mixture, which is also that of the blood, is then determined by a 

 suitable hydrometer. By the use of such methods it has been found t 

 that the specific gravity varies with age and with sex; that it is 

 diminished after eating and is increased after exercise; that it has a 

 diurnal variation, falling gradually during the day and rising slowly 

 during the night; and that it varies greatly in individuals, so that 

 a specific gravity which is normal for one may be a sign of disease 

 in another. The specific gravity of the corpuscles is slightly greater 

 than that of the plasma. For this reason the corpuscles in shed 

 blood, when its coagulation is prevented or retarded, tend to settle 

 to the bottom of the containing utensil, leaving a more or less clear 

 layer of supernatant plasma. Among themselves, also, the cor- 

 puscles differ slightly in specific gravity, the red corpuscles being 

 heaviest and the blood plates lightest. 



Red Corpuscles. The red corpuscles in man and in all the 

 mammalia, with the exception of the camel and other members of 

 the group Camelidse, are biconcave circular discs without nuclei; 

 in the Camelidse they have an elliptical form. Their average diame- 

 ter in man is given as 7.7 p. (1 // = 0.001 mm.) ; their number, which 

 is usually reckoned as so many in a cubic millimeter, varies greatly 

 under different conditions of health and disease. The average 

 number is given as 5,000,000 per c.mm. for males and 4,500,000 for 

 females. The red color of the corpuscles is due to the presence in 

 them of a pigment known as " hemoglobin." Owing to the minute 

 size of the corpuscles, their color when seen singly under the micro- 

 scope is a faint yellowish red, but when seen in mass they exhibit 

 the well-known blood-red color, which varies from scarlet in arterial 



* Hammerschlag, "Zeitschrift f. klin. Med.," 20, 444, 1892. 

 t See Jones, "Journal of Physiology," 12, 299, 1891. 



