$4 STUDENTS HISTOLOGY 



The leucocytes, especially the larger ones, are of great impor- 

 tance in pathology in connection with inflammation and the forma- 

 tion of pus. The large leucocytes furnish the great majority of 

 the cells in ordinary pus. The smaller leucocytes are about the 

 size of the red corpuscles; the larger ones are about 13 ^ in diam- 

 eter. The leucocytes are very much less numerous than the red 

 corpuscles. The ratio to the red corpuscles varies from 1 to 500 

 to 1 to 1,000. The leucocytes become more numerous a few hours 

 after eating. 



In order to study the leucocytes more carefully, they should be examined 

 in dried and stained preparations, with an oil- immersion lens if possible. 

 .Square cover-glasses are used, which need to be clean and perfectly free 

 from dust. They should be handled with forceps. Having cleaned and dried 

 the skin of the finger, puncture it quickly with a clean, sharp needle, using no 

 pressure. A drop of blood should be allowed to issue. Wipe away the first 

 drop, and use the next, which should be no larger than a pin's head. Apply 

 the surface of one cover-glass to the summit of the drop. Let this cover- 

 glass fall on the other at the angle shown in Fig. 59. The blood is spread 

 between the cover-glasses in a thin film. Quickly draw them apart, without 

 lifting. The film of blood dries immediately. The object is to spread the 

 t>lood on the cover-glass in a thin film within a few seconds after it leaves 

 the capillaries, before coagulation or changes in the shapes of the cells can 

 occur. 



To fix the preparations they should be placed in a mixture of alcohol and 

 ether -(equal parts) for half an hour; or they may be subjected to dry heat 

 (110 C.) preferably for half an hour or even longer. 



There are many methods of staining. Much can be done with the ordi- 

 nary hsematoxylin and eosin stain. Very beautiful results can be obtained 



FIG. 59. MANNER OF PLACING COVER-GLASSES. (CABOT.) 



"with combinations of aniline dyes; for instance, eosin and methylene blue: one- 

 half per cent, solution of eosin in sixty per cent, alcohol three minutes ; wash ; 

 dry, by pressing between two pieces of filter paper; strong watery solution 

 of methylene blue, one minute; wash; dry; balsam. 



The very large nucleated red blood-corpuscles of the frog and newt should 

 Ibe stained in this manner. 



