OTHER ELEMENTS OF THE BLOOD si 



On the other hand, the platelets undoubtedly stand in relation to 

 the red blood cells, since the latter can frequently be seen in the 

 apparent act of extruding from their substance globular elements 

 closely resembling the platelets in appearance and staining reaction. 



More or less apparent confusion of the subject has arisen from 

 the supposed analogy of the true blood platelets of human blood 

 with certain other structures found in the blood of the lower ver- 

 tebrates, especially the " spindle-cells " of amphibians. Eisen * has 

 cleared the matter considerably by demonstrating the presence in 

 batrachian blood of true platelets in addition to the characteristic 

 " spindle-cells." He has also shown that in at least one species 

 the true platelets represent the survival of the extruded centro- 

 some and archoplasm of the red blood cells. These platelets he 

 finds to be at first nucleated and amosboid (plasmocytoblasts) ; 

 by mitotic division the plasmocytoblasts of Eisen produce plate- 

 lets which lose their nucleus and in every way resemble the true 

 blood platelets (plasmocytes of Eisen). It is thus possible that 

 the nucleated platelets of mammalian blood are premature types, 

 and that the true platelets are genetically related to the disap- 

 pearance of the nuclei of the erythrocytes with the possible sur- 

 vival of certain of its achromatic portions. 



OTHER ELEMENTS OF THE BLOOD. Under certain condi- 

 tions the blood contains a considerable proportion of fat globules. 

 These are most abundant a few hours after a hearty meal, especially 

 if it contain an undue proportion of fatty food. The fat globules 

 which are thus found are of small size and float free in the 

 plasma. 



In addition to fat the blood has been found to contain other 

 fine granular particles which mostly represent the detritus from 

 disintegration of the blood cells. The "Wood-dust" and the 

 " hemoconia " of Miiller are of this nature. 



Plasma and Serum. Plasma is a clear colorless fluid in which 

 the formed elements of the blood are suspended. It is therefore 

 devoid of histological structure. 



Serum is likewise of a fluid nature, but differs histologically 

 from the plasma in that it contains in solution or suspension the 

 products of that disintegration of blood cells which is concomi- 

 tant with coagulation. Serum is therefore of a faint amber color 

 from the presence of hemoglobin in solution, and in addition to 



* Proc. Calif. Acad. of Sc., 1897; also, J. of Morphol., 1899. 



7' 



