BLOOD 501 



do in certain pathological conditions. After birth, erythro- 

 cytes are formed in the red marrow of bone (fig. 204). 



Marrow consists of a fine fibrous tissue with large blood 

 capillaries or sinusoids running in it. In the fibrous tissues 

 are numerous fat cells (clear spaces h in fig, 204) and 

 o-enerally a considerable number of multi-nucleated giant 

 cells {(i) and myelocytes (g). In addition t,o these are the 

 young leucocytes, leucoblasts (a.g.h.), and lastly, young 

 nucleated red cells, the erythroblasts (c.f.). After haemorrhage, 

 the formation of these becomes unusually active, and may 

 implicate parts of the marrow not generally concerned in the 

 process, and hence, the red marrow may spread from the ends 

 of the long bones, where it is usually situated, towards the 

 middle of the shaft. 



After haimorrhage, when the process of regeneration is 

 very active, red cells with nuclei, normoblasts, escape into the 

 blood. Young erythrocytes, even after they have lost their 

 nucleus, may be distinguished by a peculiar reticulated 

 appearance when they are stained with brilliant cresyl blue. 



The nuclei of the erythroblasts atrophy, and the cells 

 escape into the blood stream. 



The red marrow has the power of retaining the iron 

 of disintegrated erythrocytes, which, in different stages of 

 disintegration, are found enclosed in large modified leucocytes 

 or phagocytes. The iron is often very abundant after a 

 destruction of erythrocytes. 



VII. Total Amount of Blood in the Body. 



1. Welcker's method consists in (1) bleeding an animal, 

 measuring the amount of blood shed, and determining the 

 amount of haemoglobin contained in it; (2) then washing out 

 the blood-vessels, and, after measuring the amount of fluid 

 used, determining the amount of haemoglobin in it to 

 ascertain the amount of blood it represents. By this method 

 the amount of blood was found to be about t^ — 7-7 per cent, 

 of the body Aveight. 



2. Haldane and Lorrain Smith have devised a method 

 which can be applied to the living animal. It depends upon 



