GENERAL HISTOLOGY, 89 



longer consist of protoplasm. Embryologically they arise from 

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



Fio. 46. Red blood-corpuscles, a, of man; />, of the camel; c, of the adder; d', of 

 Proteus (seen from the edge); tl", surface view; e, of a ray; /, of Petromyzon; n, 

 nucleus (all the blood-corpuscles are magnified 700 times, except d, which is mag- 

 nified 350 times). 



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

 undertermined ; but gradually the protoplasmic cell-body changes 

 completely into a plasmic product, the stroma of the blood- 

 corpuscle. If the nucleus 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 protoplasm have disappeared. Systemati- 

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

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

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

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

 exceptions occur, since among the mammals the Typloda (camel, 

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



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 are connected with 

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

 or licemoglobin. Haemoglobin 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 

 oxygen. Haemoglobin containing oxygen, oxy-haemoglobin, causes 

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

 ' reduced ' haemoglobin causes the dark red, faintly bluish color of 

 venous blood. 



