THE BLOOD. T3 



the cell becoming almost invisible; after a time the cells lose their color 

 altogether. The cells in the figure (Fig. 69) represent the successive 

 stages of the change. A similar loss of color occurs in the red cells of 

 human blood, which, however, from the absence of nuclei, seem to dis- 

 appear entirely. 



iv. Alkalies cause the red blood-cells to swell and finally disappear. 



v. Chloroform added to the red blood-cells of the frog causes them 

 to part with their haemoglobin; the stroma of the cells becomes gradually 

 broken up. A similar effect is produced on the human red blood-cell. 



vi. Tannin. When a 'I per cent 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 (Robert's macula): the coloring matter 

 becomes at the same time concentrated in the nucleus, which grows 

 more distinct (Fig. 70). A somewhat similar effect is produced on the 

 human red blood-corpuscle. 



vii. Magenta, when applied to the red blood-cells of the frog, pro- 

 duces a similar little knob or knobs, at the same time staining the nu- 

 cleus and causing the discharge of the haemoglobin. The first effect of 

 the magenta is to cause the discharge of the haemoglobin, then the 

 nucleus becomes suddenly stained, and lastly a finely granular matter 

 issues through the wall of the corpuscle, becoming stained by the ma- 



Vf* 



?* 



FIG. 69. FIG. 70. FIG. 71. FIG. 72 FIG. 73. 



genta, and a macula is formed at the point of escape. A similar macula 

 is produced in the human red blood-cell. 



viii. Boracic acid. A 2 per cent solution applied to nucleated red 

 blood-cells (frog) will cause the concentration of all the coloring matter 

 in. the nucleus; the colored body thus formed gradually quits its central 

 position, and comes to be partly, sometimes entirely, protruded from 

 the surface of the now colorless cell (Fig. 71). The result of this ex- 

 periment led Briicke to distinguish the colored contents of the cell 

 (zooid) from its colorless stroma (oecoid). When applied to the non- 

 nucleated mammalian corpuscle its effect merely resembles that of other 

 dilute acids. 



ix. Ammonia. Its effects seem to vary according to the degree of 

 concentration. Sometimes the outline of the corpuscles becomes dis- 

 tinctly crenated; at other times the effect resembles that of boracicacid, 

 while in other cases the edges of the corpuscles begin to break up. 



Gases. Carbonic acid. - Ii the red blood-cells of a frog be first ex- 

 posed to the action of water-vapor (which renders their outer pellicle 

 more readily permeable to gases), and then acted on by carbonic acid, 

 the nuclei immediately become clearly defined and strongly granulated; 

 when air or oxygen is admitted the original appearance is at once re- 

 stored. The upper and lower cell in Fig. 72 show the effect of carbonic 

 acid; the middle one the effect of the re-admission of air. These effects 



