GENERAL HISTOL (J T. 



89 



longer consist of protoplasm. Embryo] o.oicalh' tliey arise from 

 true, nucleated, protoplasmic cells; whether these cells are iden- 



FiG. 45. — Red blood-corpuscles. . 



Vi ntcux (seen from the edge). .. , 

 nucleus ('all the blood-corpuscles a 

 uified 1350 times). 



a, of man; /j, of the camel; c, of the adder; f?', of 

 ); f/', surface view; t\ of a ray; /, of Petroniyzoni )(, 

 :-les are magnified TOO times, except tl, which'is mag- 



tical with the leucocytes or are special ' erythroblasts' is still 

 undertermined ; hut gradually the jirotoplasmic cell-body changes 

 completely into a ])lasmic product, the stroma of the blood- 

 corpuscle. If the niicleus be retained in this metamorphosis, there 

 is a slight swelling in the centre of the disc; if, however, the 

 nucleus degenerate, the bilateral convexity is replaced by a shallow 

 concavity. In the latter case, one has, in reality, no right longer 

 to speak of blood-cells, since all the characteristic constituents of 

 the cell — nucleus and ])rotop]asm — have disappeared. Systemati- 

 cally the red blood-corpuscles are of interest, since non-nucleate 

 forms are found only in the mammals (fig. 46, a, h), nucleated 

 ones in all the otlier vertebrates (c, d). The mammals also have 

 circular, the other vertebrates oval, discs. To this, iiowever, 

 exceptions occur, since among the mammals the Tyi)loda (camel, 

 llama) have oval, the Cyclostomes have circular, blood-corpnscles. 

 Haemoglobin. — The red blood-corpuscles are the cause of the 

 color of the blood, as well as the agents of one of its most impor- 

 tant functions, the interchange of gases; both arc connected with 

 the fact that the stroma contains the coloring matter of the blood 

 or luemoglobin. Hemoglobin belongs to the few crystallizable 

 proteids and is remarkable for the presence of a small, though 

 extremely important, quantity of iron, and also for its affinity for 

 oxvgen. IIa?inog]obin containing oxygen, oxy-hajmogiobin, causes 

 the carmine-like color of the so-called arterial blood; oxygen-free, 

 ' reduced ' lia?moglobiu causes the dark red, faintly bluish color of 

 venous blood. 



