LABORATORY WORK 223 



The red corpuscles, mostly collected in rouleaux (strings of 

 corpuscles stuck together by their flat sides). They appear, when 

 seen singly, to be of a faint yellow colour. 



The colourless corpuscles or leucocytes. If the cover-glass be 

 touched with a needle, they tend to stick to the glass, while the red 

 corpuscles are driven about by the current. 



Look also for fibrin filaments in the clear spaces. 



If the preparation is to be observed for any length of time, the 

 cover-glasj should have been painted around the edge with vaseline, 

 as described above (p. 166). 



An interesting preparation showing the fibrin produced in the 

 process of clotting may be made thus : Make a preparation as 

 above, and leave for ten minutes. Remove the cover-glass, run a 

 "few drops of distilled water over the slide to dissolve the corpuscles. 

 Drop on a moderately dilute solution of Spiller's purple. Leave 

 for a few minutes. Wash with distilled water. Allow to dry and 

 mount in balsam. A network of fibrin will be seen, having lumps 

 of precipitated colloid at the junctions of the filaments (so-called 

 " platelets "). (Schafer.) 



The Kidney 



Sections of the kidney of the mouse may be prepared in the 

 ordinary way. Notice the tufts of blood vessels in capsules in the 

 cortical part. These tufts can be made out better in sections of a 

 kidney of which the blood vessels have been injected with a coloured 

 material. Such sections can be bought. 



The Salts of the Blood 



Pass a 0.7 per cent, solution of pure sodium chloride in distilled 

 water through a frog's heart preparation, as described above 

 (p. 187). The beats will become weak or cease. Take 100 c.c. of 

 the solution and add 3 c.c. of o.i molar (=1.1 per cent.) calcium 

 chloride. Pass through the heart. The beats increase in size, but 

 the heart tends to become tonically contracted, shown by incom- 

 plete relaxation between the beats. Take another 100 c.c. of the 

 sodium chloride solution, add 3 c.c. of the calcium chloride solution 

 and also 6 c.c. of o.i molar ( = 0.75 per cent.) solution of potassium 

 chloride. Pass through the heart. The beats become vigorous 

 with normal relaxation. Pass again the pure sodium chloride. 

 When the beats have become small, take 100 c.c. of the solution 

 and add 6 c.c. of the potassium chloride solution. No improvement 

 results. Hence all these three cations sodium potassium, and 



