40 THE CIRCULATING LIQUIDS OF THE BODY 



of the red corpuscles is diminished; and the ratio of white to red 

 may approach 1:4. As the anaemia rapidly advances towards the 

 fatal termination of an acute case, and the erythrocyte count falls to 

 1,000,000, or even less, the ratio may come still nearer to unity. An 

 increase in the number of leucocytes has also been observed in cer- 

 tain infective diseases as part of the inflammatory reaction. There 

 are also physiological variations, even within short periods of time ; 

 for example, the number of lymphocytes is increased when digestion 

 is going on (digestive lymphocytosis) . The normal number of 

 blood-plates varies from a quarter to half a million to the cubic 

 millimetre, but may be greater in disease and at high levels 

 (Kemp). 



Life-History of the Corpuscles. The corpuscles of the blood, like 

 the body itself , fulfil the allotted round of life, and then die. They 

 arise, perform their functions for a time, and disappear. But 

 although the place and mode of their origin, the seat of their destruc- 

 tion or decay, and the average length of their life, have been the 

 subject of active research and still more active discussion for many 

 years, much yet remains unsettled. 



Origin of the Erythrocytes. In the embryo the red corpuscles, even 

 of those forms (mammals) which have non-nucleated corpuscles in 

 adult life, are at first possessed of nuclei, and approximately spherical 

 in form. In the human foetus, at the fourth week all the red corpuscles 

 are nucleated. Later on the nucleated corpuscles gradually diminish 

 in number, and at birth they have almost or altogether disappeared, 

 some of them, at least, having been converted by a shrivelling of the 

 nucleus into the ordinary non-nucleated form. In the newly born rat, 

 which comes into the world in a comparatively immature state, many 

 of the red corpuscles may be seen to be still nucleated. The first cor- 

 puscles formed in embryonic life are developed outside of the embryo 

 altogether. Even before the heart has as yet begun to beat, certain 

 cells of the mesoderm (see Chapter XIX.) in a zone (' vascular area ') 

 around the growing embryo begin to sprout into long, anastomosing 

 processes, which afterwards become hollowed out to form capillary 

 bloodvessels. At the same time clumps of nuclei, formed by division 

 of the original nuclei of the cells, gather at the nodes of the network. 

 Around each nucleus clings a little lump of protoplasm, which soon 

 develops haemoglobin in its substance; and the new-made corpuscles 

 float away within the new-made vessels, where they rapidly multiply 

 by mitosis. In later embryonic life the nucleated corpuscles continue 

 in part to be developed within the bloodvessels in the liver, allantois, 

 spleen, and red bone-marrow, and in certain localities in the connective 

 tissue, by mitotic division of previously existing nucleated corpuscles, 

 in part to be formed endogenously within special cells in the liver and 

 perhaps other organs. Still later the nucleated corpuscles give place in 

 the blood of the mammal to non-nucleated erythrocytes. Many of 

 these are doubtless derived from the nucleated corpuscles, but some 

 appear to be produced in the interior of certain cells of the connective 

 tissue, and are non-nucleated from the start. 



In the mammal in extra-uterine life the chief seat of formation 

 of the red blood-corpuscles, or haematopoiesis, is the red marrow of 



