134 THE BLOOD 



Chloroform and Ether. These reagents when added to the red blood 

 cells of the frog cause them to part with their hemoglobin; the stroma of the 

 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 (zooid) 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, powdered vermilion, 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 and ex- 

 amine 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 are said to 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 



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 Nachet, Gowers) of known capacity, and the number of corpus- 

 cles 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' modi- 



