80 THE BLOOD 



believed to form pseudopodial-like processes, the ends of which are 

 pinched off and pass into the blood stream as platelets. Develop- 

 ing and degenerating megakaryocytes are to be foimd in red marrow. 

 The Destruction of Blood Cells. — The different tyjjes of blood cells 

 apparently have diff'ering periods of life. Some are relatively short 

 lived, as the erythrocytes of mammals which have an estimated life 

 of about thirty days, but others may live over much longer i)eriods. 

 It has been observed that many red cells are phagocytized l)y histio- 

 cytes, the macrophages, in the red pulp of the spleen; in certain 

 pathological conditions so many are destroyed that the red pulp 

 becomes brown in color. Old granulocytes are also apparently 

 phagocytized by Kupffer cells, the macrophages in the liver. The 

 lymphocytes are continually degenerating in lymph tissue and 

 many are lost as a result of their migration through the epithelial 

 lining of the alimentary tract and various other ducts. 



REFERENCES. 



Dawson, A. B. 1931. Supravital studies on the erythrocyte of the catfish 

 (Ameiurus nebulosus, Lesureur ), with special reference to the Nittis stigma, 

 Anat. Rec, 49, 121. 



1932. The reaction of the erythrocytes of vertebrates, especially 



fishes, to vital dyes, Biol. Bull., 63, 48. 



1933. A reinterpretation of the findings of Komocki (1932) on the 



blood on the Urodele (Batrachoseps attenuatus), Anat. Rec, 58, 31. 



1935. The hemopoietic response in the catfish, Ameiuris nebulosus. 



to chronic lead poisoning, Biol. Bull , 68, 335. 

 JoRDON, H. E. 1932. The histology of the blood and the blood-forming 



tissues of the Urodele (Proteus anguineus), Am. Jour. Anat., 51, 215. 

 1933. The evolution of blood-forming tissues. Quart. Rev. Biol., 



8, 58. 



18, 1. 



1934. Extramedullary erythrocytopoiesis in man, Arch. Path., 



1934. The transformation of adipose tissue into hemocytopoietic 



tissue, Anat. Rec, 59, 461. 

 JoRD.\N, H. E., .\ND Flipper, ,1. C. 1913. Hematopoiesis in chelonia, Folia 



ha?matol., 15, 1. 

 JoRD.'VN, H. E., AND SpEiDEL, C. C. 1930. Blood formation in Cyclostomes, 



Am. Jour. Anat., 216, 355. 

 ■ 1931. Blood formation in the .\frican hmgtish, under normal 



conditions and under conditions of prolonged esti\ation and recovery. 



Jour. Mori)h., 51, 319. 

 Kindred, J. E. 1932. A study of the tinctorial reaction of hemoglobiniferous 



cells, Russell body cell, plasma cells and lymphocytes of the albino rat by 



a new method of selective staining, Anat. Rec, 53, 43. 

 Mayer.son, H. S. 1930. The blood cytology of dogs, Anat. Rec, 47, 239. 

 Redfield, a. C. 1933. The evolution of the respiratory function of the blood, 



(iuart. Rev. Biol., 8, 58. 

 Sabin, F. 1928. Bone-marrow, Physiol. Rev., 8, 191. 



See Appendix for general text references. 



