The development of the human body; a manual of human embryology . o that there is a necessity for the formation ofnew corpuscles and for the existence of haematopoieticorgans at all stages of life. In the fetus erythrocytes in process of division may befound in the general circulation and even in the heartitself, but they are much more plentiful in places wherethe blood-pressure is diminished, as, for instance, in thelarger capillaries of the lower limbs and in the capillaries ofall the visceral organs and of the subcutaneous organs, however, such as the liver, the spleen, andt
The development of the human body; a manual of human embryology . o that there is a necessity for the formation ofnew corpuscles and for the existence of haematopoieticorgans at all stages of life. In the fetus erythrocytes in process of division may befound in the general circulation and even in the heartitself, but they are much more plentiful in places wherethe blood-pressure is diminished, as, for instance, in thelarger capillaries of the lower limbs and in the capillaries ofall the visceral organs and of the subcutaneous organs, however, such as the liver, the spleen, andthe bone-marrow, present especially favorable conditionsfor the multiplication of the blood-cells, and in these notonly are the capillaries enlarged so as to afford resting-places for the corpuscles, but gaps appear in the wallsof the vessels through which the blood-elements maypass and so come into intimate relations with the actualtissues of the organs (Fig. 123). Afterbirth the haemat-opoietic function of the liver ceases and that of the spleen THE BLOOD. 245. becomes limited to the formation of white corpuscles,though the complete function may be re-established incases of extreme anaemia. The bone-marrow, however,retains the func-tion completely, beingthroughout life theseat of formation ofboth red and whitecorpuscles, the lymph-atic nodes and folli-cles, as well as thespleen, assisting in theformation of the latterelements. Until about the sec-ond month of develop-ment the erythrocytes and leukocytes are the Fl*;- 123.—Section of a Portion of the J . Liver of a Rabbit Embryo of 5 mm. Only elements found in e> Erythrocytes in the liver substance the blood, and in the haematopoietic organs they may be observed in active mitosis. In addition other cells, having the same general appearance as the erythocytes but lacking haemoglobin, also occur, and these, which may be termed0A erythroblasts, produce by division erythrocytes in which haemoglobin gradu- Fig. 124.—Stages in
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
