THE BLOOD 7 



red blood-disc, the life of which is probably only a matter of a 

 few days, gets worn out and dies. In this condition it is cast off 

 from the system, being got rid of through the medium of the 

 4- liver. In addition to the blood-stream, other suggested seats of 

 destruction are the spleen, bone-marrow, and lymph-glands, but 

 no definite statement can at present be made. When the red 

 cells die; their haemoglobin is set free, and decomposed into an 

 iron-free residue from which, probably, all the pigments of the 

 body are formed, certainly those of the bile. 



The seat of formation of the red cells is in the red marrow of 

 bones, where they are formed from certain nucleated colourless 

 cells ; there are several varieties of blood-forming cells (erythro- 

 blasts) in the red marrow, and it is not definitely settled which 

 of these furnish the red blood-cells. All other seats of formation 

 are doubtful. In the embryo the future red cells for a certain 

 period are nucleated and contain no haemoglobin, but these are 

 gradually replaced by non-nucleated, haemoglobin-holding cor- 

 puscles before birth. It is interesting to observe that both in 

 the embryo and in the adult the red cells are derived from a 

 nucleated precursor. 



By the time the corpuscle takes its place in the blood as a cell 

 which has lost its nucleus it is on the downward path. This and 

 other considerations have assigned its probable life in the blood- 

 stream as only a matter of a few days. 



Haemolysis. — It has been pointed out that in a normal con- 

 dition the haemoglobin is contained wholly within the red cells, 

 and that there is no passage of colouring matter from the cells 

 to the fluid in which they are carried. Anything which kills the 

 red cell, or, if we adopt the cell-wall view, anything which kills 

 the envelope, allows the haemoglobin to escape. 



The cells may be destroyed by alternately freezing and thawing 

 the blood, or by the passage through it of electric shocks, or by 

 the addition of certain agents such as chloroform, ether, bile salts, 

 tannic or boric acids, etc. The haemoglobin becomes liberated 

 from the bro ken-up cells, and stains the naturally yellow plasma 

 a red colour. The blood under these circumstances, as we have 

 seen, is no longer opaque, but transparent, and the term ' laky ' 

 well describes its colour. The entire process is described as 

 1 haemolysis.' 



Most of the above causes of haemolysis act as protoplasmic 

 poisons ; they kill the cell, and as the osmotic pressure of the 

 plasma is slightly less than that of the corpuscular contents, the 

 haemoglobin diffuses out. Poisons such as ether and chloroform 

 are probably haemolytic owing to their chemical effect in dissolv- 

 ing the cholesterin and lecithin of the corpuscles. Others may 

 unite with these substances and render them soluble, by which 



