BLOOD Si 



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. 

 i. 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 oj blood from the heart of a frog ; 

 dilute it with a drop of normal salt solution (0'75 per cent.) ; put 

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

 vent evaporation : exam,ine 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 YTirv ^ twwu "^^ ^^ inch, 

 ii. WMte 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 

 intervals of half a minute. 



2. Action of acetic acid on blood. 



Place afresh drop of blood on a clean slide : add a drop of 

 acetic add : cover, and examine with the high power : note the 

 changes produced. 



i. Red corpuscles : the nuclei become much more 

 apparent than before, and the red colour dis- 

 appears. 



