88 NORMAL HISTOLOGY. 



LYMPH. 



In lymph, in addition to the plasma from which 

 fibrin is formed on separation from the body, we 

 find spheroidal cells identical in structure with the 

 white blood-cells ; sometimes a few red blood-cells ; 

 and variously shaped granules or minute globules, 

 composed apparently of a combination of albu- 

 minoid material, with fat. These globules, in that 

 variety of lymph called chyle, are so abundant as to 

 give the fluid a milky appearance. 



Origin of Blood-cells. Direct observation has 

 shown that, in some animals at least, the white 

 blood-cells can multiply by division. Whether the 

 cells which supply the place of those which seem 

 to be used up in the process of growth and repara- 

 tion are produced in this way, and if so, whether 

 the division occurs in the blood- or lymph-vessels, 

 or in the cell-spaces of the connective tissue, or in 

 certain special organs, or whether they are pro- 

 duced in a manner entirely unknown to us these 

 are questions not only of theoretical but of practi- 

 cal interest ; but, in spite of much research, and the 

 accumulation of many observations bearing on the 

 matter, we are still unable to give them a definite 

 answer. Still more obscure, if possible, is the origin 

 of the red blood-cells. Although in the adult man they 

 seem to possess no nucleus, yet in embryonic life 

 they certainly are furnished with that structure ; we 

 find nucleated red blood-cells. Now, it has been re- 



