34 NUMBER OF RED CORPUSCLES. [BOOK i. 



25. The average number of red corpuscles in human blood 

 may be probably put down at about 5 millions in a cubic milli- 

 metre (the range in different mammals is said to be from 3 to 18 

 millions), but the relation of corpuscle to plasma varies a good deal 

 even in health, and very much in disease. Obviously the relation 

 may be affected (1) by an increase or decrease of the plasma, (2) by 

 an actual decrease or increase of red corpuscles. Now the former 

 must frequently take place. The blood as we have already urged 

 is always being acted upon by changes in the tissues and indeed 

 is an index of those changes ; hence the plasma must be con- 

 tinually changing, though always striving to return to the normal 

 condition. Thus when a large quantity of water is discharged by 

 the kidney, the skin or the bowels, that water comes really from 

 the blood, and the drain of water must tend to diminish the bulk 

 of the plasma, and so to increase the relative number of red cor- 

 puscles, though the effect is probably soon remedied by the passage 

 of water from the tissues into the blood. So again when a large 

 quantity of water is drunk, this passes into the blood and tends 

 temporarily to dilute the plasma (and so to diminish the relative 

 number of red corpuscles) though this condition is in turn soon 

 remedied by the passage of the superfluous fluid to the tissues 

 and excretory organs. The greater or less number of red corpuscles 

 then in a given bulk of blood may be simply due to less or more 

 plasma, but we have reason to think that the actual number of 

 the corpuscles in the blood does vary from time to time. This 

 is especially seen in certain forms of disease, which may be spoken 

 of under the general term of anaemia (there being several kinds 

 of anaemia) in which the number of red corpuscles is distinctly 

 diminished. 



The redness of blood may however be influenced not only by 

 the number of red corpuscles in each cubic millimetre of blood but 

 also by the amount of haemoglobin in each corpuscle, and to a less 

 degree by the size of the corpuscles. If we compare, with a common 

 standard, the redness of two specimens of blood unequally red, 

 and then determine the relative number of corpuscles in each, we 

 may find that the less red specimen has as many corpuscles as the 

 redder one, or at least the deficiency in redness is greater than can 

 be accounted for by the paucity of red corpuscles. Obviously in 

 such a case the red corpuscles have too little haemoglobin. In 

 some cases of anaemia the deficiency of haemoglobin in each cor- 

 puscle is more striking than the scantiness of red corpuscles. 



The number of corpuscles in a specimen of blood is determined by 

 mixing a small but carefully measured quantity of the blood with a large 

 quantity of some indifferent fluid, e.g. a 5 p.c. solution of sodium 

 sulphate, and then actually counting the corpuscles in a known 

 minimal bulk of the mixture. 



This perhaps may be most conveniently done by the method generally 

 known as that of Gowers (Haemacytometer) improved by Malassez. A 



