212 



RED CORPUSCLES OF THE LOWER VERTEBRATA. 



crystallization. The crystals present various forms in different animals, but almost all (the 

 hexagonal plates of the squirrel being- alone excepted) belong to the rhombic system. From 

 human blood and that of most mammals, the crystals are elongated prisms (fig. 243. 1), but they 

 are tetrahedrons in the guinea-pig (2), and short rhombohedrons in the hamster (4). They are 

 most readily obtained for microscopical examination from the blood of the rat, where they 

 appear merely on adding a little water, and afterwards evaporating. 



All haemoglobin crystals contain a certain amount of water of crystallization. They 

 are doubly refracting (anisotropous). The spectrum of haemoglobin, whether in substance 

 or in solution, may be always readily recognized by the double or single absorption bands, 

 which are produced according as it is present in the oxidated or deoxidated condition. 



Other coloured crystals, which may be obtained from blood, are the so-called " ha3min 

 crystals " of Teichmann. They are formed when hasmoglobin is warmed with a little salt and 

 glacial acetic acid. On cooling, the haamin crystallizes out in minute reddish brown acicular 

 prisms (fig. 244), the demonstration of which affords a positive proof of the presence of blood- 

 colouring matter. They may readily be obtained from dried blood without the addition of salt, 

 merely by warming it with glacial acetic acid. 



The amount of hasmoglobin in each corpuscle, which is liable to variation, may be approxi- 

 mately arrived at by determining both the number of corpuscles and the amount of hasmoglobin 

 in a given volume of blood. The amount of haemoglobin is estimated by diluting a sample of 

 blood with a known amount of water, and comparing the tint of the solution so obtained with 

 that of a solution of haemoglobin of known strength. A very convenient means of quickly 

 obtaining an idea of the amount of haemoglobin in a sample of blood is afforded by the 

 " hEemoglobinometer " of Gowers, which is arranged on the above principle. 



Structure of the nucleated red corpuscles of the lower vertebrata. 



The large corpuscles of the frog (fig. 245) and newt differ from the mammalian 



Fig. 245. FROG'S BLOOD (Ranvier). 



a, red corpuscle seen on the flat ; v, vacuole 

 in a corpuscle ; b, c, red corpuscles in profile ; 

 n, pale corpuscle at rest ; TO, pale corpuscle, 

 exhibiting amoeboid movements ; p, colourless 

 fusiform corpuscle. 



corpuscles in the possession of a nucleus. 

 It is rather more than one-third the 

 length of the corpuscle, but in the 

 natural unaltered condition is visible 

 with difficulty ; this is probably owing 

 to the fact that it possesses very nearly 

 the same index of refraction as the rest 

 of the corpuscle. For it may be ren- 

 dered visible, even under such circum- 

 stances, by the combined action of 



watery vapour and carbonic acid upon the blood ; a precipitate (of serum-globulin ?) 

 is thus produced upon the nucleus, and its outline comes into view: on readmission 

 of air the precipitate is re-dissolved, and the nucleus again becomes faint or 

 disappears (Strieker). 



The effect of most reagents is similar to that produced on human blood. Water 

 causes both corpuscle and nucleus to swell up by imbibition, the coloured part being 

 then extracted. A dilute solution of acetic acid in an indifferent fluid also removes 

 the colouring matter, but the nucleus presents a markedly granular appearance 

 (fig. 240, 3) ; if strong acetic acid be employed, the nucleus often acquires a reddish 

 tint. Alkalies, on the other hand, even when very dilute, rapidly destroy both 

 corpuscle and nucleus. Various reagents added to newt's blood cause the coloured 

 part of the corpuscles to become partly withdrawn from the envelope, and collected 

 around the nucleus ; this is especially the case with a solution of boracic acid, 

 the coloured matter and nucleus ("zooid" of Briicke) may subsequently be alto- 

 gether extruded from the envelope or stroma of the corpuscle (" oecoid "). 



