BLOOD. 357 



appear to have a dark spot in the middle. In the frog the glo- 

 bules are six times as large as in man. In the blood of that ani- 

 mal it is easy, he says, to show that the globule is not perforated 

 as Torre supposed ; but that the dark spot is a little solid body, 

 which is contained in the middle of a vesicle. Hence, he calls 

 the globules red vesicles, each, according to him, being a flat ve- 

 sicle, with a small solid sphere in its centre. When a little wa- 

 ter is added to the blood, the vesicles swell and become round, 

 and if the glass plate on which they are lying be placed oblique- 

 ly, they may be seen running down it, while the little central so- 

 lid may be seen falling from side to side like a pea in a bladder. 

 Water gradually dissolves the red vesicles, leaving the central 

 solid undissolved, But if a little salt be added to the water, the 

 vesicles become flat, and do not dissolve. 



Hewson conceived that the use of the thymus and lymphatic 

 glands was to form the central solids, and that the vesicles which 

 surround them are formed in the spleen. 



But this hypothesis respecting the formation of the red glo- 

 bules has not been confirmed by later observers. Nor has 

 Hewson's account of the shape and structure of these globules been 

 admitted as exact. They seem to be flat ellipsoids, and the notion 

 of their being.vesicles containing a central nucleus has not been 

 adopted. 



In the blood of the frog, where the globules are six times as 

 large as in human blood, the globules may be separated from 

 the serum by the filter. In all red-blooded animals the globules 

 may, by careful washing, be deprived of their colour. The red 

 colouring matter dissolves in the water, but the globules re- 

 main undissolved, and assume a whitish colour.* 



Lecanu has shown by experiments seemingly decisive, that the 

 globules of blood consist at least of three distinct substances, 

 namely, hematosin, albumen, and fibrin, and that the weight of 

 hematosin does not exceed ^h P ai *t of that of the globule. ( 

 The fibrin, in his opinion, constitutes the outer surface of the glo- 

 bules, and envelopes a compound of hematosin and albumen, 

 which has been generally taken for the colouring matter of blood. 



* Mr Gulliver has examined and described the globules in a great number of 

 animals. His valuable results may be seen in the Philosophical Magazine, (3d 

 series) xvi. 23, 105, 195. They are too long and too little connected with che- 

 mistry to find a place here. 



t Etudes Chimiques sur le Sang Humain, p, 48. 



