il8 BLOOD AND LYMPH, 



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 corpuscles 

 differ slightly in specific gravity, the red corpuscles being heaviest. 



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

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

 the group Camelidae, are biconcave circular discs or, according to 

 some authors, bell-shaped corpuscles without nuclei; in the Cam- 

 elidae they have an elliptical form. Their average diameter in 

 man is given as 7.7 /i (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 

 blood to purplish red in venous blood, this variation in color being 

 dependent upon the amount of oxygen contained in the blood in 

 combination with the hemoglobin. Speaking generally, the func- 

 tion of the red corpuscles is to carry oxygen from the lungs to the 

 tissues. This function is entirely dependent upon the presence of 

 hemoglobin, which has the power of combining easily with oxygen 

 gas. The physiology of the red corpuscles, therefore, is largely con- 

 tained in a description of the properties of hemoglobin. 



Condition of the Hemoglobin m the Corpuscle. — ^The finer structure 

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



