CHAP, i.] BLOOD. 45 



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

 tissue arranged as a delicate network. The meshes of this are 

 crowded with colourless nucleated 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 shew 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, leu- 

 cocytes 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 dis- 

 tinct 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 lymphatics 

 are continually bringing to the blood an abundant supply of 

 leucocytes, and that these in the blood become ordinary white 

 corpuscles. This is probably the chief source of the white cor- 

 puscles, 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 continu- 

 ally being added to the blood, white corpuscles must as continually 

 either be destroyed, or be transformed, or escape from the interior 

 of the blood vessels ; otherwise the blood would soon be blocked 

 with white corpuscles. 



Some do leave the blood vessels. 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 blood vessels into spaces filled 

 with lymph, the "lymph spaces," as they are called, of the tissue 

 lying outside the blood vessels. This is spoken of as the " migra- 

 tion 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 corpuscles may, by following the devious tracts of 

 the lymph, find their way back into the blood ; some of them how- 

 ever may remain, and undergo various changes. Thus, in inflamed 

 areas, when suppuration follows inflammation, 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 perma- 

 nent 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 



