22 THE CIRCULATING LIQUIDS OF THE BODY 



erythrocytes may also take place in the spleen and bone-marrow. 

 Although the statement that free blood-pigment exists in demon- 

 strable amount in the plasma of the splenic vein is incorrect, red 

 corpuscles have been seen in various stages of decomposition within 

 large amoeboid cells in the splenic pulp; and deposits containing 

 iron have been found there and in the red bone-marrow in certain 

 pathological conditions. But there is no good foundation for the 

 statement sometimes rather fancifully made that the spleen is in 

 any special sense the ' graveyard of the red corpuscles.' Some of 

 the coloured corpuscles may break up in the blood itself, forming 

 granules of pigment, which may then be taken up by the liver, spleen, 

 and lymph glands. Indeed, it is probable that a large proportion 

 of the worn-out erythrocytes are finally destroyed in the blood- 

 stream. The portal circulation may be more than other vascular 

 tracts a seat of this natural decay, perhaps in virtue of the presence 

 of substances with a hsemolytic action (p. 28) absorbed from the 

 alimentary canal. 



It has been argued that the erythrocytes must be short-lived, 

 since they are devoid of nuclei (p. 6), and attempts have been 

 made to calculate the average time for which they survive in the 

 circulation from the amount of haemoglobin (or of its derivative, 

 haematin) required to furnish the daily excretion of bile-pigment. 

 The results arrived at, however, are not sufficiently trustworthy to 

 warrant their citation. 



Origin and Fate of the Leucocytes. There has been much dis- 

 cussion as to the origin of the white blood-corpuscles. The 

 numerous theories fall into two groups, which have been designated 

 somewhat pompously the monistic and the dualistic. According 

 to the first, all the colourless corpuscles arise from a single type 

 of parent cell, namely, the lymphocyte type, in its small or large 

 variety. According to the dualistic school, a fundamental distinc- 

 tion exists between the lymphocytes, or cells peculiar to lymphoid 

 tissues, and to the blood on the one hand, and the remaining varieties 

 of leucocytes on the other. The former are supposed to be derived 

 from the lymphoblasts of lymphoid tissue, and the latter from the 

 myeloblasts, the forerunners of the myelocytes of bone-marrow. 

 The question has recently been studied by Foot by a new method, 

 namely, by cultivating chicken marrow outside of the body, and 

 watching the transformation of certain of its cells. He concludes 

 in favour of the development of the polymorphonuclear leucocyte 

 from a lymphoid type of cell existing in the marrow, a conclusion 

 in harmony with the monistic view. As regards their immediate 

 source, the small lymphocytes of the blood are undoubtedly derived 

 from the lymph, and are identical with the lymph-corpuscles. 

 That they are formed largely in the lymphatic glands is shown 

 by the fact that the lymph coming to the glands is much poorer 



