420 THE BLOOD. [CH. XXM. 



multi-nucleated, finely granular corpuscles are the most vigorous 

 phagocytes. The accompanying figure illustrates this; the cells 

 represented, however, are not leucocytes, but the large amoeboid 

 cells found in connective tissues, especially in inflamed parts. 

 (See also p. 275.) 



The process of emigration of the leucocytes is described on 

 p. 274. 



Action of Reagents on the colourless corpuscles. Water causes 

 the corpuscles to swell and their nuclei to become apparent. 

 Acetic acid (i per cent.) has a similar action; it also causes the 

 granules to aggregate round the nucleus (fig. 350). Dilute 

 alkalis produce swelling and bursting of the corpuscles. 



The Blood-Platelets. 



Besides the two principal varieties of blood-corpuscles, a third 

 kind has been described under the name blood-platelets (Blut- 

 pldtchen). These are colourless disc-shaped or irregular bodies, 

 much smaller than red corpuscles. Different views are held as to 

 their origin. At first they were regarded as immature red cor- 

 puscles ; but this view is discarded. They may be disintegrative 

 products of white corpuscles ; some state that they are merely a 

 precipitate of nucleo-proteid which occurs when the plasma dies 

 or is cooled. There is, however, no doubt that they do occur in 

 living blood. 



Enumeration of the Blood-Corpuscles. 



Several methods are employed for counting the blood-corpuscles ; most of 

 them depend upon the same principle, i.e., the dilution of a minute volume 

 of blood with a given volume of a colourless saline solution similar in 

 specific gravity to blood plasma, so that the size and shape of the cor- 

 puscles is 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 & 

 Nachet, 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' 

 modification, by the division of the cell area into squares of known size. 

 Having ascertained the number of corpuscles in the diluted blood, it is 

 easy to find out the number in a given volume of normal blood. 



Gowers' Hcemacytometer consists of a small pipette (A), which, when 

 filled up to a mark on its stem, holds 995 cubic millimetres. It is 

 furnished with an india-rubber tube and glass mouth-piece to facilitate 

 filling and emptying ; a capillary tube (B) marked to hold 5 cubic 

 millimetres, and also furnished with an india-rubber tube and mouth- 

 piece ; a small glass jar (D) in which the dilution of the blood is performed ; 

 a glass stirrer CE) for mixing the blood and salt solution thoroughly ; (F) a 

 needle, the length of which can be regulated by a screw ; a brass stage 

 plate (c) carrying a glass slide, on which is a cell one-fifth of a millimetre 



