THE CORPUSCLES OF THE BLOOD. 49 



are more numerous in the lymphatic vessels after these have passed through 

 the lymphatic glands. These lymphatic glands are partly composed of 

 what is known as adenoid tissue, a special kind of connective tissue arranged 

 as a delicate network. The meshes of this are crowded with colorless nucle- 

 ated cells, which, though varying in size, are, for the most part, small, the 

 nucleus being surrounded by a relatively small quantity of cell substance. 

 Many of these cells show signs that they are undergoing cell-division, and 

 we have reason to think that cells so formed, acquiring a larger amount of 

 cell substance, become veritable leucocytes. In other words, leucocytes 

 multiply in the lymphatic glands, and leaving the glands by the lymphatic 

 vessels, make their way to the blood. Patches and tracts of similar adenoid 

 tissue, not arranged, however, as distinct glands, but similarly occupied by 

 developing leucocytes and similarly connected with lymphatic vessels, are 

 found in various parts of the body, especially in the mucous membranes. 

 Hence we may conclude that from various parts of the body, the lymph- 

 atics are continually bringing to the blood an abundant supply of leuco- 

 cytes, and that these in the blood become ordinary white corpuscles. This 

 is probably the chief source of the white corpuscles, for though the white 

 corpuscles have been seen dividing in the blood itself, no large increase 

 takes place in that way. 



32. It follows that since white corpuscles are thus continually being 

 added to the blood, white corpuscles must as continually either be destroyed, 

 or be transformed, or escape from the interior of the bloodvessels ; otherwise 

 the blood would soon be blocked with white corpuscles. 



Some do leave the bloodvessels. In treating of the circulation we shall 

 have to point out that white corpuscles are able to pierce the walls of the 

 capillaries and minute veins, and thus to make their way from the interior 

 of the bloodvessels into spaces filled with lymph, the " lymph spaces," as- 

 they are called, of the tissue lying outside the bloodvessels. This is spoken 

 of as the " migration of the white corpuscles." In an "inflamed area" 

 large numbers of white corpuscles are thus drained away from the blood 

 into the lymph spaces of the tissue ; and it is probable that a similar loss 

 takes place, more or less, under normal conditions. These migrating cor- 

 puscles may, by following the devious tracks of the lymph, find their way 

 back into the blood ; some of them, however, may remain, and undergo 

 various changes. Thus, in inflamed areas, when suppuration follows in- 

 flammation, the white corpuscles which have migrated may become " pus 

 corpuscles," or, where thickening and growth follow upon inflammation, 

 may, according to many authorities, become transformed into temporary or 

 permanent tissue, especially connective tissue ; but this transformation into 

 tissue is disputed. When an inflammation subsides without leaving any 

 effect a few corpuscles only will be found in the tissue; those which had 

 previously migrated must, therefore, have been disposed of in some way or 

 another. 



In speaking of the formation of red corpuscles ( 27) we saw that not 

 only it is not proved that the nucleated corpuscles which give rise to red 

 corpuscles are ordinary white corpuscles, but that in all probability the real 

 hsematoblasts, the parents of red corpuscles, are special corpuscles developed 

 in the situations where the manufacture of red corpuscles takes place. So 

 far, therefore, from assuming, as is sometimes done, that the white corpuscles 

 of the blood are all of them on their way to become red corpuscles, it may 

 be doubted whether any of them are. In any case, however, even making 

 allowance for those which migrate, a very considerable number of the white 

 corpuscles must " disappear " in some way or other from the blood stream, 

 and we may, perhaps, speak of their disappearance as being a " destruction " 



