154 TH E BLOOD 



cells becomes gradually broken up. A similar effect is produced on the 

 human red blood-cell. 



Tannin and Boric Acid. When a 2 per cent, fresh solution of tannic acid 

 is applied to frog's blood it causes the appearance of a sharply denned little 

 knob, projecting from the free surface (Roberts' macula). The coloring 

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

 more distinct, figure 128. A somewhat similar effect is produced on the 

 human red blood corpuscle. 



A 2 per cent, solution of boric acid applied to nucleated red blood-cells of 

 the 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, figure 129. The result of this experiment led Briicke to dis- 

 tinguish the colored contents of the cell (zob'id) from its colorless stroma 

 (ecoid). When applied to the non- nucleated mammalian corpuscle its effect 

 merely resembles that of other dilute acids. 



3. Phagocytosis in White Corpuscles. Mix some very fine pigment 

 granules, bacterial emulsion, or charcoal with a few drops of frog's blood, 

 let stand for 10 or 20 minutes, then mount a drop on the glass slide or 

 make a smear and stain and examine under a high- magnifying microscope. 

 In a favorable field here and there will be found some white corpuscles 

 which have taken up the pigment. Colored corpuscles have been observed 

 with fragments of pigment embedded in their substance. White corpuscles 

 have also been seen in diseased states of the body to contain micro-organisms, 

 for example, bacilli and have the power of destroying these organisms, which 

 gives them the name phagocytes. 



4. Enumeration of the Blood Corpuscles. Several methods are 

 employed for counting the blood corpuscles, most of them depending upon 



m 



FIG. 130. Thoma-Zeiss Hemacytometer, glass slide. 



the same principle; i.e., the dilution of a minute volume of blood with a 

 given volume of a colorless solution similar in specific gravity to blood plasma, 

 so that the size and shape of the corpuscles are altered as little as possible. 

 A minute quantity of the well-mixed solution is then taken, examined under 

 the microscope, either in a flattened capillary tube (Malassez) or in a cell 

 (Hayem and Nache, Gowers) of known capacity, and the number of 

 corpuscles in a measured length of the tube or in a given area of the cell 

 is counted. The length of the tube and the area of the cell are ascertained 

 by means of a micrometer scale in the microscope ocular; or, in the case of 

 Gowers's modification, by the division of the cell area into squares of known 



