118 HISTOLOGY. 



and cannot be found in an ordinary fresh blood specimen. 

 Clumps of debris, which probably represent their remains, arc 

 seea-usually. By pricking the finger through a drop of osmic 

 acid or methyl-violet, these bodies can be preserved. The 

 number in 1 cubic millimetre is given by some authors as 

 200,000, by others as much as 635,000. 



Everywhere in normal human blood there are small rat 

 globules and other fine colorless granules, known as blood dust 

 or hwmokonien (H. F. Miiller). Their size is usually less than 

 1^, and their function and significance are unknown. The fat 

 globules probably come from the chyle. 



Hislogenesis of Blood. 



Concerning the development of blood-cells there is a great 

 diversity of opinion. Some authors claim that they are of 

 mesodermal origin, while others trace their origin to the ento- 

 derm. There is also discussion as to whether or not red and 

 white blood-cells have the same origin. 



We shall, first of all, speak of the development of the red 

 corpuscles of mammals. The cells from which these arise, the 

 so-called erythroblasts, are round nucleated cells somewhat 

 larger than the erythrocyte, possessing a homogeneous proto- 

 plasm which contains hsemoglobin. The origin of the erythro- 

 blasts and the way in which they acquire their hemoglobin arc 

 not known definitely. They, however, increase by indirect 

 division and pass over into the form of erythrocytes. In 

 mammals this involves the loss of the nucleus, for in the new- 

 born all the red blood-cells are non-nucleated, while in em- 

 bryos the majority of the blood-corpuscles possess nuclei. 

 Some authors believe that the nucleus is simply extruded from 

 the cell, and have not only followed all stages in the extrusion, 

 but also have observed free nuclei in the blood. Other inves- 

 tigators, on the contrary, claim that the nucleus disintegrates 

 in the cell and disappears. 



The development of red blood-corpuscles in embryonal life 

 takes place in the liver, the walls of the umbilical vesicle, the 

 lymph glands (exceptionally), the spleen pulp, and the bone- 



