12 THE BLOOD. 



swell up, become spherical, and are finally lost to view by solution. The same effect 

 follows almost instantaneously on the addition of acetic acid. 



Structure. The structure of the blood-corpuscles is very simple. They are perfectly 

 homogeneous, presenting, in their normal condition, no nuclei or granules, and are not 

 provided with an investing membrane. A great deal has been said by anatomists con- 

 cerning this latter point ; and some are of the opinion that the corpuscles are cellular in their 

 structure, being composed of a membrane, with viscid, semifluid contents. Without going 

 fully into the discussion of this question, it may be stated that few have assumed to have 

 actually demonstrated this membrane ; but certain observers have inferred its existence 

 from the fact of the corpuscles swelling, and, as they term it, bursting on the addition 

 of water. The appearances presented upon the addition of iodine to blood previously 

 treated with water, which have been supposed to indicate the presence of shreds of 

 ruptured vesicles, are not sufficiently distinct to demonstrate the existence of a membrane. 

 The great elasticity of the corpuscles, the persistence with which they preserve their 

 biconcave form, and their general appearance, rather favor the idea that they are homo- 

 geneous bodies of a definite shape, than that they have a cell-wall with semifluid con- 

 tents ; especially as the existence of a membrane has been only inferred and not posi- 

 tively demonstrated. Their mode of nutrition is like that of other anatomical elements. 

 They are bathed in a nutritive fluid, the plasma, and, as fast as their substance becomes 

 worn out and effete, new material is supplied. In this way, they undergo the same 

 molecular changes as other anatomical structures. When destroyed or removed from the 

 body in hemorrhages, new corpuscles are gradually developed, until their quantity 

 reaches the normal standard. 



Development of the Blood- Corpuscles. Very early in the development of the ovum, 

 the blood-vessels appear, constituting what is called the area vasculosa. At about the 

 same time, the blood-corpuscles are developed, it may be before, or it may be just after the 

 appearance of the vessels, for this point is undetermined. The blood becomes red when 

 the embryon is about one-tenth of an inch in length. From this time until the end of 

 the sixth or eighth week, they are from thirty to one hundred per cent, larger than in 

 the adult. Most of them are circular, but some are ovoid, and a few are globular. At 

 this period, nearly all of them are provided with a nucleus ; but, from the first, there are 

 some in which this is wanting. The nucleus is from y^-g- to -g-^Vo f an mcn m diameter, 

 globular, granular, and insoluble in water and acetic acid. As development advances, 

 these nucleated corpuscles are gradually lost ; but, even at the fourth month, we may 

 still see a few remaining. After this time, they present no anatomical differences from 

 the blood-corpuscles in the adult. 



In many works on physiology and general anatomy, we find accounts of the develop- 

 ment of the red corpuscles from the colorless corpuscles, or leucocytes, which are sup- 

 posed to become disintegrated, their particles becoming developed into red corpuscles ; 

 but there seems to be no positive evidence that such a process takes place. The red cor- 

 puscles appear before the leucocytes are formed ; and it is only the fact that the two 

 varieties coexist in the blood-vessels which has given rise to such a theory. It is most 

 reasonable to consider that the red corpuscles are formed by a true genesis in the san- 

 guineous blastema. There is, farthermore, no sufficient evidence that any particular 

 organ or organs have the function of producing the blood-corpuscles. It is regarded by 

 some as a necessity that there should be an organ for the destruction of the corpuscles, 

 and one for their formation. Eegarding them, as we certainly must, as organized bodies 

 which are essential anatomical elements of the blood, it is difficult to imagine what 

 reasons, based on their function, should lead physiologists to seek so persistently after an 

 organ for their destruction. The hypothesis that they are used in the formation of pig- 

 mentary matter seems hardly sufficient to account for this. The observations of Malassez, 



