THE BLOOD. 57 



which is in truth blood in its primitive form, it is in those 

 fluids, doubtless, that they take their origin, and it is in them 

 that they are best studied. 



Origin of the Red Globules. It has already been shown that 

 Donne and others consider that the red globules are formed 

 out of the white, which they view as true blood globules which 

 have not reached the last degree of elaboration. Donne sustains 

 this opinion by reference to the following particulars : First, 

 that amongst the red globules contained in a single drop of 

 blood, all are not affected to the same extent by the use of the 

 same re-agent; that some resist its influence for a much 

 longer period than others ; Secondly, he states, that he has 

 observed, in some true blood globules traces of a slight 

 punctuation, similar to that which is seen in the white cor- 

 puscles ; and, Thirdly, in certain white globules he has noticed 

 the compressed form common to the red corpuscles. From 

 the observation of these facts he draws the conclusion, that 

 the white globules are transformed into red blood discs. 

 The first particular alluded to, viz. that the same re-agent 

 does not affect equally all the red globules of the same blood, 

 is doubtless to some extent correct, and may be explained by 

 supposing that the red corpuscles are not all of the same age, 

 and therefore are of different degrees of consistence. The 

 remarks as to the granular texture of true blood corpuscles, 

 and the compressed form of certain white globules, it has 

 never happened to me to be able to verify in a single instance ; 

 and, for my own part, therefore, I am inclined to allow to 

 them but very little weight in determining the question of 

 the origin of the red corpuscles of the blood. To the views 

 of M. Donne on this point a high degree of plausibility and 

 ingenuity must certainly be accorded ; but, in considering this 

 question, not merely the doubtful and even debateable nature 

 of the evidence adduced by M. Donne must be taken into 

 consideration, but also the following fact, viz., that no defi- 

 nite relation exists in the animal kingdom between the size 

 of the red and white globules compared together. In man, 

 and most mammalia, the white globules are larger than the 

 red (see Plate \.fiy* 1.) ; in most reptiles, and particularly 



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