THE FORMED CONSTITUENTS OF THE BLOOD 149 



(The body surface of a grown man is only about 2 sq. m.) This enormous 

 extent of surface' of the red blood corpuscles is of great significance in con- 

 nection with their function in respiration (Chapter IX). 



Moreover the number of red blood corpuscles in 1 cu. mm. of blood varies 

 not a little under perfectly normal circumstances. Some authors have observed 

 an increase, others a decrease in the number after meals. There is substantial 

 agreement, however, that complete or partial abstinence from food does not 

 reduce the number. Rarefaction of the air, as on mountain tops, increases the 

 number of red corpuscles per cubic millimeter of blood very considerably, and 

 the effect is not due to an excessive elimination of water from the body, for 

 the same thing has been noted on animals where an increased transpiration of 

 water was impossible. The increase has been regarded as an attempt on the 

 part of the organism to offset incomplete saturation of the blood with oxygen, 

 resulting from lower air pressure. But this explanation does not suffice, for 

 the increase takes place just the same before the reduction of pressure is suffi- 

 cient to affect the absorption of oxygen. 



It should be remarked in connection with these and other normal variations 

 in the number of red blood corpuscles, that blood-counts give us only the rela- 

 tive number, and do not throw any light on the total number of corpuscles. 

 For it must not be forgotten that under some circumstances the relative num- 

 ber of corpuscles in different parts of the body varies greatly (Zuntz), nor that 

 an exudation of plasma from the vessels may produce an apparent increase 

 (Bunge) in short, it is not an easy matter properly and exactly to estimate 

 the total number of blood corpuscles. 



The specific gravity of the red corpuscles (1.008-1.105) is greater than 

 that of the plasma or of the serum (the sp. grr of the latter in man amounts 

 to about 1.017). Hence they sink to the bottom of a vessel in which the blood 

 is caught, provided we are dealing with whipped blood, or blood whose coagu- 

 lation is artificially stopped or retarded. Since the separation of the blood 

 corpuscles from the plasma or serum can be accomplished much more rapidly 

 with the centrifuge than by mere settling, this instrument is often used in 

 blood work. 



On the addition of very small quantities of most acids or acid salts of 

 Fe, Al, Zn, Cu, Hg, Sn, Ag, Au, Ur, Mb, the red blood corpuscles become 

 agglutinated, and thereby precipitated. The same takes place even with hasmo- 

 globin-free stromata as well as with the leucocytes, and is probably caused 

 by an effect on the contained globulin (Peskind). 



The weight of the red blood corpuscles in 100 parts of blood is estimated, 

 according to Alex. Schmidt, in the following manner: (1) The percentage of 

 dry residue (T) in the whole blood is determined; (2) the percentage of dry 

 residue (t) in the serum belonging to this quantity of blood; (3) the dry resi- 

 due (r) of the red blood corpuscles obtained from 100 g. of blood. The dry 

 residue of the serum obtained from 100 g. of blood is then T <r, and the 



100 X (T 7') 



corresponding quantity of serum is : -, so that the weight of the 



100 X (T T) 



red llood corpuscles in 100 parts of blood is 100 -. 



t 



