13.2 ELEMENTABT PHYSIOLOGY. [XII. 



digits. Stick two pins into the board a little 

 distance from the hole; by twining the cotton 

 round them the web may be stretched out level 

 above the hole (or the toes may simply be pinned 

 out). Surround the web, and cover the leg and 

 body of the frog, with moist blotting-paper. 

 Put a small drop of water upon the web, and 

 cover it with a triangular piece of cover-slip, 

 taking care that the glass does not cut into the 

 digits and that no fluid flows over it. 

 Examine, first with a low and then with a high 

 power. Note 



a. The course of the blood from the arteries to 

 the veins. A slight pulsation may be ob- 

 served in the larger arteries and sometimes 

 in the smaller ones. 



h. The greater velocity of the blood in the 

 arteries (owing to their smaller size) than 

 in the veins; probably in neither caii the 

 individual corpuscles be made out. 



c. The axial and peripheral zones in the arteries 

 and veins ; the peripheral zone is small, and 

 under a low power appears free from corpus- 

 cles; under a high power one or two white 

 corpuscles may, if the current is not very 

 fast, be seen in the peripheral zone of the 

 arteries; in that of the veins a few white 

 corpuscles and occasionally a red one will be 

 seen moving along comparatively slowly. 



d. The passage of corpuscles usually in single 

 file through the capillaries ; 



