Il] BLOOD CORPUSCLES OF FROG 19 



Examine at once. Note the elongated pale cells (plate- 

 lets) about ^ the size of the red corpuscles. Some are 

 found singly, others sticking together in groups. The 

 nucleus can generally be made out, it is large in com- 

 parison with the amount of cell-substance. The nucleus 

 soon becomes round and the cell-substance indistinct. 



16. Examine (h. p.) a drop of fluid containing blood 

 stained with methyl-violet. The nuclei of all the 

 elements of the blood are stained rather deeply ; the 

 cell-substance of the white corpuscles and of the 

 platelets takes a light stain. 



The fluid is obtained as follows : Let a drop of fresh blood of a 

 frog or newt fall into 5 c.c. of a filtered mixture containing 0'6 p.c. 

 NaCl, O'Gp.c. peptone and 0'02 p.c. methyl -violet, stir at once. Place 

 the mixture in a small glass tube and centrifugalize for a few minutes, 

 pour off about 4 c.c. of the fluid. Shake up the rest and examine a 

 drop. The platelets are preserved for some hours, but soon the 

 nucleus becomes round, the cell- substance puts out hyaline blebs, 

 and in time the cell disintegrates. In the absence of a centrifugal 

 machine the mixture should be allowed to stand for an hour, and 

 the lower layers taken for examination. 



17. The platelets and other corpuscles of the blood are best 

 preserved by allowing a drop of blood to run into 5 c.c. of a mixture 

 containing 0'5 p.c. osmic acid, and O75 p.c. NaCl. 



The mixture is centrifugalized, most of the supernatant fluid 

 poured off, the corpuscles shaken up in the remainder. If a little of 

 this be examined, the platelets are seen to be elongated and the 

 white corpuscles for the most part spherical. 



A film preparation may be made by spreading a drop on a cover- 

 slip, and drying it on a warm bath. It can be stained and mounted 

 in the usual way, but the staining of the various cells differs but little 

 and is predominantly basic, so that the time of stay in the basic-stains 

 must be lessened. 



The cells may be stained in bulk, either with stains soluble in 



22 



