BLOOD 37 



vertebra, and beneath the shoulder girdle : 

 they open into the subscapular veins. 



b. The posterior lymph hearts lie at the sides of 

 the urostyle, close to its hinder end. They 

 communicate by short vessels with the 

 femoral veins. Their pulsations can easily 

 be seen in a pithed frog. 

 4. The spleen has been already referred to (p. 23). 



F. Microscopic Examination of Blood. 

 I. Frog's Blood. 

 1. Normal. 



Place on a slide a small drop of blood from the heart of a frog ; 

 dilute it with a drop of normal salt solution (Q'75per cent.) ; put 

 on a thin cover-glass, and run a ring of oil round the edge to 

 prevent evaporation : examine with the high power. 



Blood consists of a colourless fluid, the liquor sanguinis 

 or plasma, in which float the blood corpuscles. These 

 corpuscles are of two kinds. 



i. Red corpuscles. These are very numerous, pale 

 red or yellowish red in colour, and of a flattened 

 oval shape, with rounded edges and a central 

 bulging, the nucleus. The flattened shape is best 

 seen when a corpuscle turns edgeways. They 

 measure 0*0235 mm. in length by 0'0145 mm. in 

 width ; or about yyVff x YSW ^ an i ncn - 



ii." White corpuscles. These are much fewer in number 

 and of smaller size : they are colourless, granular, 

 subspherical in shape, and exhibit " amoeboid " 

 movements. Sketch one half a dozen times at inter- 

 vals of half a minute. 



In order to find the white corpuscles, focus the red corpuscles 

 as sharply as possible ; then on turning the screw of the fine 

 adjustment slightly, so as to throw t/iem just out of focus, the 

 white corpuscles stand out as blurred white points (owing to l/ieir 

 refracting light more strongly) ; when thus found, focus down- 

 wards again, and study them. 



