THE BLOOD-CORPUSCLES 21 



the bones of the skull and trunk, and of the ends of the long bones 

 of the limbs. Special nucleated cells in the marrow, originally 

 colourless, multiply by karyokinesis, take up haemoglobin or, what 

 is much more likely, form it within their protoplasm, and are 

 transformed by various stages into the ordinary non-nucleated red 

 corpuscles, which then pass into the blood-stream. These blood- 

 forming cells have received the name of erythroblasts or haemato- 

 blasts. According to their size, erythroblasts have been distinguished 

 as normoblasts, megaloblasts, and microblasts. The normo- 

 blasts are most numerous, and have about the same diameter as 

 the full-formed erythrocytes, into which they are believed to 

 develop. The megaloblasts are larger, and the microblasts smaller, 

 and they are thought to be the precursors of those aberrant forms 

 of erythrocytes sometimes found in the blood in certain diseases 

 After haemorrhage rapid regeneration of the blood takes place, so 

 that in a few weeks the loss of even as much as a third of the total 

 blood is made good. The plasma is much sooner restored to its 

 normal amount than the corpuscles. Microscopical examination 

 shows in the red marrow the tokens of increased production of 

 coloured corpuscles, and nucleated erythrocytes appear in the 

 blood, the normoblasts being, as it were, hurried into the circula- 

 tion before the transformation which normally results in the dis- 

 appearance of the nucleus is complete. The same is true in 

 severe pathological anaemias, e.g., pernicious anaemia. It is a 

 matter of interest that other organs also, which in embryonic 

 life perform a haematopoietic function, particularly the spleen, 

 may, in such emergencies, again take on the office of forming 

 blood-corpuscles. 



A constant destruction of red blood-corpuscles must go on, for 

 the bile-pigment and the pigments of the urine are derived from 

 blood-pigment. The bile-pigment is formed in the liver. It con- 

 tains no iron; but the liver cells are rich in iron, and on treatment 

 with hydrochloric acid and potassium ferrocyanide, a section of 

 liver is coloured by Prussian blue. Iron must therefore be 

 removed by the liver from the blood-pigment or from one of its 

 derivatives ; and there is other evidence that the liver is either one 

 of the places in which red corpuscles are actually destroyed, or 

 receiyes blood charged with the products of their destruction. 

 Although it cannot be doubted that in all animals whose blood 

 contains haemoglobin the iron found in the liver bears an important 

 relation to the building up or breaking down of the blood-pigment, 

 the injection of haemoglobin or haemin, indeed, increasing markedly 

 the amount of iron in the liver, as well as in the spleen, bone-marrow 

 and other tissues, this does not seem to be the only function of the 

 hepatic iron, for the liver of the crayfish and the lobster, which 

 have no haemoglobin in their blood, is rich in iron. Destruction of 



