CIL XXIX.] 



THE BLOOD-CORPUSCLES 



455 



by their ends, and cluster; so that, when the blood is spread out thinly 

 on a glass they form an irregular network (fig. 318). 



. . FIG. 319. Corpuscles of the frog. The 



* 10. 318.-Red corpuscles in rouleaux. The central mass consists of nucleated 



white corpuscles are uncoloured. coloured corpuscles. The other cor- 



puscles are two varieties of the 

 colourless form. 



Action of Reagents. Considerable light has been thrown on the physical and 

 chemical constitution of red blood-cells by studying the effects produced by 

 mechanical means and by various reagents ; the following is a brief summary of 

 these reactions : 



Water. When water is added gradually to frog's blood, the oval disc-shaped 

 corpuscles become spherical, and gradually discharge their haemoglobin, a pale, 

 transparent envelope being left behind : human red blood-cells swell, change 

 from a discoidal to a spheroidal form, burst and discharge their pigment, becoming 

 quite transparent and all but invisible. This effect is due to osmosis. 



Physiological saline solution causes no effect on the red corpuscles beyond pre- 

 venting them running into rouleaux. If a stronger salt solution is used, the cor- 

 puscles shrink and become crenated (fig. 320), owing to osmosis of water outwards. 

 Dilute acetic acid causes the nucleus of the red blood-cells in 

 $k <tfk the frog to become more clearly defined ; if the action is pro- 



longed, the nucleus becomes strongly granulated, and all the 

 colouring matter seems to be concentrated in it, the surrounding 

 cell-substance and outline of the cell becoming almost invisible ; 

 after a time the cells lose their colour altogether. A similar 

 loss of colour occurs in the red corpuscles of human blood, 

 which, however, from the absence of nuclei, seem to disappear 

 entirely. 



Dilute alkalis cause the red blood-cells to dissolve slowly, and finally to disappear. 

 Chloroform, ether, and other reagents that dissolve fats dissolve the lipoid 

 subs f ances (lecithin, etc.) of the membrane which surrounds the 

 corpuscles, and so produce taking of the blood. 



Tannic acid. When a 2 per cent, fresh solution of tannic 

 acid is applied to frog's blood it causes the appearance of a 

 sharply-defined little knob, projecting from the free surface 

 (Roberts' macula) : the colouring matter becomes at the same 

 time concentrated in the nucleus, which grows more distinct 

 (fig. 321). A somewhat similar effect is produced on the human 

 red blood-corpuscle, the colouring matter being discharged 

 and coagulated as a little knob of haematin on the surface of the corpuscle. 



FIG. 320.-Effect 

 of saline solu- 

 tion (crena- 

 tion). 



FIG. 321. Effect of 

 tannin. 



