THE CIRCULATING LIQUIDS OF THE BODY 21 



limbs. Special nucleated cells in the marrow, originally colour- 

 less, multiply by karyokinesis, take up haemoglobin or 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 haematoblasts. According to their 

 size, erythroblasts have been distinguished as normoblasts, 

 megaloblasts, and microblasts. The normoblasts 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. Other organs also, par- 

 ticularly the spleen, may, in such emergencies, take on a blood- 

 forming function. 



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 contains 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 receives 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 erythrocytes may 

 also take place in the spleen and bone-marrow. Although the 

 statement that free blood-pigment exists in demonstrable amount 

 in the plasma of the splenic vein is incorrect, red corpuscles have 

 been seen in various stages of decomposition within large amoeboid 

 cells in the splenic pulp ; and deposits containing iron have been 

 found there and in the red bone-marrow in certain pathological 



