264 James Homer Wright. 



3. The blood platelets are derived from certain parts or constituents 

 of the red blood cell other than the extruded nucleus. 



Various theories are grouped under this heading. The funda- 

 mental objection to all of them is that the most approved methods 

 of preparation fail to give satisfactory evidence that the red blood 

 cell at any period in its development contains a body which sug- 

 gests a blood platelet and do not show any transitions between 

 red blood corpuscles or their fragments and the blood platelets. 

 Occasionally in smear preparations a blood platelet may be seen 

 lying upon a red cell and this appearance has been interpreted as 

 showing that the blood platelet is first contained within a red 

 blood corpuscle, then later is extruded. In sections, in which the 

 blood platelets are characteristically stained, I have never seen 

 a blood platelet within a red blood corpuscle. The view that some, 

 if not all of the blood platelets, are pinched-ofT portions or frag- 

 ments of the red cells which have undergone certain changes 

 whereby they present the characteristic staining and structure, 

 which are brought out by the modern methods of preparation, 

 is a pure assumption of fact to explain the obvious differences 

 between fragments of red blood corpuscles and blood platelets. 

 Fragments of red blood corpuscles, or so-called blood platelets 

 containing hemoglobin, practically do not occur in the normal 

 blood. 



4. The blood platelets are a definite and independent kind of 

 blood cell. 



This is open to the objection that the blood platelet has no 

 nucleus. The central granular portion brought out by proper 

 staining methods cannot be regarded as a nucleus as has been 

 maintained because it lacks the definite structure of a nucleus 

 and the characteristic affinity for nuclear dyes. 



5. The blood platelets are not independent cells or cell fragments 

 but are of the nature of albuminous precipitates. 



Against this view may be urged the characteristic appearances 

 and structure of the blood platelets as brought out by various 

 methods of preparation and the fact, confirmed by personal 

 observation, that the blood platelets under certain conditions show 

 continuous and amoeba-like change in form and outline. 



