THE BLOOD CORPUSCLES. 141 



Erythrocytes. : The red corpuscles, or eryfkrocytes, as they 

 are called, are by far the most numerous, there being five mil- 

 lion of them in a cubic millimetre of normal blood. Examined 

 under the microscope, they are seen to be flattened, bi-concave, 

 non-nucleated discs in man; but in the embryo, as well as in 

 birds and reptiles, they have a nucleus. Each corpuscle consists 

 of an envelope and a framework of protein and lipoid material 

 containing a substance known as haemoglobin. 



HAEMOGLOBIN is a very complex body, belonging to the general 

 class of conjugated proteins (see p. 21). Haemoglobin has the 

 ability to unite with large amounts of oxygen, thus enabling 

 the blood to carry the oxygen gathered in the lungs, to the dis- 

 tant tissues. It consists of a combination of a simple protein, 

 globin, and a pigment, haematin. Hcematin contains iron, which 

 is responsible for the ability of oxygen to unite with the haemo- 

 globin molecule. The combination of haemoglobin with oxygen 

 is not very stable, and can be readily broken with the liberation 

 of oxygen. It is for this reason that this molecule is adapted to 

 carry oxygen to the tissues. The quantity of haemoglobin held 

 by the corpuscle may vary and in some diseases, as in chloro- 

 anaemia, for instance, it may be greatly diminished, so much so 

 that the tissues may be unable to obtain the proper amount of 

 oxygen. The amount of haemoglobin actually present in a sample 

 of blood may be estimated by the intensity of the red color it 

 gives to the blood. To estimate this intensity a drop of blood 

 is received on blotting paper, the stain being then compared 

 either with that produced by normal blood in various dilutions 

 on the same paper, or with a standardized chart. From the con- 

 centration of normal blood whose stain most nearly matches that 

 of the unknown sample, we can determine the percentage of 

 haemoglobin in the latter, or we can read this directly from the 

 chart. 



ENUMERATION OF THE BLOOD CORPUSCLES. The number of red 

 or white cells present in a cubic millimetre of blood may be esti- 

 mated by the use of a haemacytometer or blood-counter. This 

 consists of two mixing capillary tubes, in one of which the blood 

 is diluted one hundred times with saline solution, and in the 



