186 PHYSIOLOGY. 



cells. The primitive corpuscles are spherical in shape, nucleated, 

 and possess amoeboid movements. They undergo multiplication by 

 karyokinesis. 



During the f cetal period the protoplasm of the -connective-tissue 

 corpuscles, derived from the mesoblast, contains cells of the size and 

 appearance of blood-corpuscles. The mother-cells elongate, throw 

 out processes which become hollowed out and branched until they 

 reach the regular circulatory vessels, with which they unite to empty 

 into them their fluid and cells. During this period also they seem 

 to be developed from the liver, spleen, and red bone-marrow. 



During Extra-uterine Life. For some time after the birth of 

 the mammal, nonnucleated corpuscles are still formed in the spleen, 

 liver, and connective-tissue cells, but by far the most important and 

 prolific seat is in the red marrow of bones. It is in the bones of the 

 skull, trunk, and ends of the long bones that blood-formation is 

 most extensive, since the shafts of these bones contain a yellow, 

 fatty substance which is nonproductive. Within the marrow are 

 seen numbers of nucleated, red cells, which are very similar to the 

 corpuscles of the embryo, and which, like them, multiply by karyo- 

 kinesis. From these repeated divisions there result nonnucleated 

 red corpuscles which are washed into the circulation. The blood- 

 forming cells have received the name of erytliroblasts, and they are 

 particularly numerous after copious haemorrhage, when the lost blood 

 is "being replaced by more active formation. At such times some 

 erythroblasts may appear in the blood-stream, having been forced 

 out prematurely, so active is the function of the red marrow in 

 striving to repair the damage done. These soon lose their nuclei 

 while in the blood-stream. If the loss by haemorrhage has been par- 

 ticularly severe, the yellow bone-marrow and spleen assist in blood- 

 manufacture, for in the latter and in the splenic vein are found 

 nucleated, red corpuscles identical with those of the red marrow of 

 bone. 



DESTRUCTION OF THE RED CORPUSCLES. 



The student can gain some comprehension of the number of cor- 

 puscles which must constantly be undergoing disintegration when 

 he recalls the fact that all of the pigmentary matters in the body 

 owe their existence, directly or indirectly, to the haemoglobin of 

 these little bodies. The quantities of urinary and biliary pigments 

 alone that are excreted from the economy are considerable. 



Physiologists have proved that there are fewer red corpuscles 



