874 PHYSIOLOGY 



It was stated some years ago by Menzies that a solution of impure 

 haemochromogen, prepared by the action of ammonium sulphide on alkaline 

 haematin obtained in the ordinary way from blood, on standing for some 

 days was reconverted into reduced haemoglobin. Ham and Balean have 

 confirmed this observation, and have shown in addition that haemo- 

 chromogen, prepared by the action of ammonium sulphide on an alkaline 

 solution of pure haemin, though perfectly stable by itself, 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 haemochromogen 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 surrounds the blastoderm and 

 will later become the area vasculosa, presents on examination under the 

 low power a network of anastomising 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- multi- 

 plying 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 siirroundniij; 

 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 cor- 

 puscles are of the non-nucleated type. These however 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. 375). The formation 

 of red corpuscles does not cease with the end of foetal life or even with the 



