THE RED BLOOD-CORPUSCLES 939 



was rapidly reconverted into haemoglobin if a solution of globin were 

 added to the mixture. The same change took place if egg-white were 

 used instead of globin. The haemoglobin thus formed was changed into 

 oxyhaemoglobin on shaking with air. Although in these experiments the 

 oxyhaemoglobin was not separated in the crystalline form, its colour 

 and spectral characters are so very distinctive that we are justified 

 in concluding not only that it is possible to effect a recombination of 

 the haamochromogen and globin, but also that other proteins can take 

 the place of globin in the haemoglobin molecule. 



THE LIFE-HISTORY OF THE RED BLOOD-CORPUSCLES 



The growth of the embryo as well as of the young animal must be 

 attended with a continual increase in the number of red blood- 

 corpuscles present in the body. In the developing embryo the first 

 formation of red corpuscles occurs in the vascular area. In the chick, 

 about the twentieth hour of incubation, the area opaca, which sur- 

 rounds the blastoderm, and will later become the area vasculosa, 

 presents on examination under the low power a network of anasto- 

 mising strands more opaque than the rest of the area. On section 

 these strands are seen to be made up of cellular masses, the ordinary 

 mesenchyma, with branched cells and amoeboid corpuscles lying 

 between. The cells in these cords are continually multiplying by 

 indirect division. Those on the outer side of the cord become the 

 endothelium of dilated blood-vessels, while those in the interior acquire 

 a yellowish colour from the laying down of haemoglobin in their 

 cytoplasm. The cords become canalised, and, as soon as a connection 

 is established with the vascular system of the embryo, the newly 

 formed blood-corpuscles move slowly on into the general circulation. 

 The red corpuscles in the bird are true erythrocytes, i.e. are nucleated 

 cells. The leucocytes seem to arise by the immigration of wandering 

 cells from the surrounding mesenchyma. Other places in the foetus 

 where a similar growth of corpuscles proceeds throughout foetal life 

 are the liver and the spleen, and later on the bone-marrow. 



In the mammal the nucleated erythrocytes, though forming the 

 majority of the red corpuscles in early foetal life, become fewer and 

 fewer in number as gestation advances, so that at birth practically the 

 whole of the corpuscles are of the non-nucleated type. These, how- 

 ever, can be shown to be derived from nucleated red corpuscles by a 

 process either of extrusion or of degeneration and solution of the 

 nucleus (Fig. 360). The formation of red corpuscles does not cease with 

 the end of foetal life or even with the attainment of full stature by the 

 animal. We have definite proof that a continual formation of red 

 corpuscles can proceed and is proceeding throughout the whole of 



