222 THE BLOOD. 



size of the globules would give every opportunity for detecting any 

 such changes, did they really exist ; and it is our unavoidable con- 

 clusion from these observations, that there is no good evidence, even 

 in the blood of reptiles, of any such transformation taking place. 

 There is simply, as in human blood, a certain variation in size and 

 opacity among the red globules; but no such connection with, or 

 resemblance to, the white globules as to indicate a passage from one 

 form to the other. The red and white globules are therefore to be 

 regarded as distinct and independent anatomical elements. They 

 are mingled together in the blood, just as capillary bloodvessels and 

 nerves are mingled in areolar tissue ; but there is no other connection 

 between them, so far as their formation is concerned, than that of 

 juxtaposition. 



Neither is it at all probable that the red globules are produced or 

 destroyed in any particular part of the body. One ground for the 

 belief that these bodies were produced by a metamorphosis of the 

 white globules was a supposition that they were continually and 

 rapidly destroyed somewhere in the circulation ; and as this loss 

 must be as rapidly counterbalanced by the formation of new glo- 

 bules, and as no other probable source of their reproduction ap- 

 peared, they were supposed to be produced by transformation of 

 the white globules. But there is no reason for believing that the 

 red globules of the blood are any less permanent, as anatomical 

 forms, than the muscular fibres or the nervous filaments. They 

 undergo, it is true, like all the constituent parts of the body, a 

 constant interstitial metamorphosis. They absorb incessantly nu- 

 tritious materials from the blood, and give up to the circulating 

 fluid, at the same time, other substances which result from their 

 internal waste and disintegration. But they do not, so far as we 

 know, perish bodily in any part of the circulation. It is not the 

 anatomical forms, anywhere, which undergo destruction and reno- 

 vation in the nutritive process ; but only the proximate principles of 

 which they are composed. The effect of this interstitial nutrition, 

 therefore, in the blood-globules as in the various solid tissues, is 

 merely to maintain them in a natural and healthy condition of 

 integrity. Their ingredients are incessantly altered, by transforma- 

 tion and decomposition, as they pass through various parts of the 

 vascular system; but the globules themselves retain their form 

 and texture, and still remain as constituent parts of the circulating 

 fluid. 



