364 THE AMERICAN MONTHLY [Dec, 



The latter brings fortli distinctly the reticular structure 

 of fully developed red blood corpuscles. The smallest 

 haematoblasts under the influence of these solutions are 

 either unchanged or exhibit a small central or excentric 

 vacuole whereby the hsematoblast is rendered ring shaped. 



Hsematoblasts up to half the diameter of a red blood 

 corpuscle resist, at least for some time, a solution of 

 glacial acetic acid with equal parts of water. They retain 

 both a yellow tint and a smooth contour, whereas fully 

 developed red blood corpuscles by this reagent are either 

 rendered flat, much enlarged, corrugated into many 

 shapes, or broken up as will be described later. 



The smallest hsematoblasts always retain a smooth sur- 

 face, even though the red blood corpuscles in the same 

 specimen have become crenated all over. When the 

 hsematoblasts have reached about half the size of fully 

 developed red blood corpuscles they assume a finely 

 crenated surface, the crenations appearing like needle 

 shaped projections from their margins, and not blunt, or 

 knob-like, as are those of fully developed red blood cor- 

 puscles. 



As to their origin I shall not make positive statements 

 for the present. I am sure however, that the old opin- 

 ion as to the origin of red blood corpuscles from color- 

 less corpuscles is erroneous. Haematoblasts are formed 

 in the tissues of the embryo, or the fcetus whenever one 

 type of connective tissue changes into another, for in- 

 stance, cartilage into bone. Haematoblasts are formed 

 whenever in the process of development of the tissues 

 new blood vessels arise. They are formed in the adult 

 in all lymph structures, mainly in the lymph ganglia and 

 in the spleen throughout life. The older a person grows 

 the less of lymphatic structure is present in the organ- 

 ism, hence haematoblasts are found only in small num- 

 bers in the blood of very aged people. Final statements 

 as to the origin of haematoblasts I leave until I have fin- 



