38 THE VASCULAR SYSTEM OF THE FROG 



2. Action of acetic acid on blood. 



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

 acetic acid : cover, and examine with the high power : note t/ie 

 changes produced. 



i. Eed corpuscles: the nuclei become much more 

 apparent than before, and the red colour disappears. 

 ii. White corpuscles : become clearer, and show nuclei, 

 sometimes more than one in a single corpuscle. 



II. Human Blood. 



1. Normal. 



Prick the tip of your finger, and place a small drop of t/te 

 blood on a slide : add a drop of normal salt solution, cover, and 

 examine as before. Note the following points : 



i. Red corpuscles. These, which are much smaller 

 than in frog's blood, are in the form of circular 

 biconcave discs with rounded edges but no nuclei. 

 They have a tendency to run together into rou- 

 leaux, like piles of coins. Their average diameter 

 is O'OOS mm., or about $^QQ of an inch. 



ii. White corpuscles. These are very similar to those 

 of the frog : they are slightly larger than the red 

 corpuscles, averaging about O'Ol mm., or -j-gVff ^ an 

 inch in diameter : their amoeboid movements are 

 not well seen unless the slide is warmed. 



2. Action of acetic acid. 



Treat with acetic acid as before : note that, unlike the frog's 

 blood, no nuclei are visible in the red corpuscles. 



0. Circulation of the Blood in the Web of a Frog's Foot. 



The web uniting the toes of the frog's foot is so thin and 

 transparent, that with the microscope the blood in it can readily 

 be seen coursing along the capillaries, 



Examine a frog prepared to show the_ circulation in the web of 

 the foot. Note the following points : 



1. With a low power. 



a. The irregularly branched pigment cells to which the 

 colour of the frog's skin is due. 



