THE BLOOD 15 



qtiently referred to as blood-leucocytes. They are not all of one 

 kind ; there are microscopical differences in their structure which 

 has enabled a classification to be made, and though this is by 

 no means final, particularly in face of the limited knowledge 

 possessed regarding these cells, yet it is useful as a means of 

 identification and description. Ehrlich regards the white 

 corpuscles as divisible into two main groups — lymphocytes 

 and leucocytes. The former are distinguished by the cell-body 

 being free from granules, while amoeboid movement may be 

 characteristically absent. The opposite condition exists in 

 leucocytes. 



Two varieties of Lymphocytes are described in the blood — 

 small and large. The former, the size of a red cell, represents 

 about one quarter of all the white corpuscles ; the latter, two or 

 three times larger in size, do not represent more than 1 per cent, 

 of the whole. 



Three varieties of Leucocytes are described — polynuclear, or 

 polymorphonuclear, which represent the bulk of tne white 

 blood-cells, with a sub-group known as eosinophiles ; uninuclear 

 occurring to the extent of from 2 to 10 per cent, of the white cells ; 

 and mast-cells, which represent less than 1 per cent. Not only 

 the nature of the nucleus, but also the reaction which the cell 

 granules give with dyes, enables these groups to be distinguished 

 from each other. The granules of the uninuclear cell readily 

 stain with neutral dyes ; the polynuclear cells stain with neutral 

 or acid dyes, while the mast-cells demand basic dyes. Some 

 leucocytes and lymphocytes may be seen in Plate I., 2. 



The origin of the lymphocytes and leucocytes has been 

 variously attributed to lymphatic tissue and bone-marrow, but 

 very little is at present known of the subject. There is a free 

 communication between the lymphatic system and the blood via 

 the thoracic duct, and though a mixture of material gains access 

 to the blood by this route, there is no doubt that much of it is 

 pure lymph. 



The white corpuscles contain about 10 per cent, of solids. The 

 cell protoplasm consists of proteins belonging to the globulin 

 and nucleo-protein groups, while the nucleus consists of nuclein 

 which is remarkable as being a very stable substance, and also 

 as containing phosphorus. The effect of nucleo-protein when 

 injected into the circulation will be dealt with at p. 21. 



The white corpuscles, as well as the red, are constantly being 

 used up and as constantly replaced. They also possess, as we 

 have seen, the power of passing through the walls of the vessels 

 into the surrounding tissues, from which they are removed by 

 the lymph channels, and so find their way back to the blood. 

 No doubt many corpuscles leave the blood, for whose destruction 



