104 PRACTICAL HISTOLOGY. 



first stunned by a blow on the head, so that no pain can 

 possibly be produced, and then a vertical incision is made 

 on the left side of the abdomen ; a vein immediately below 

 the axilla must be avoided, and also the stomach and 

 duodenum. The small intestine is gently drawn out with 

 forceps, and fixed with small pins to a crescent of cork close 

 to a window (B, Fig. 44) in the cardboard. If the ex- 



FIG. 44. Frog-plate of cardboard. The slits c and d are only used when the 

 frog is not curarised and requires to be secured in a bag. 



amination is to extend over a considerable time, a thick 

 cover-glass should be fixed with sealing-wax to the glass on 

 the cork, leaving, however, the outer half of the latter exposed. 

 The mesentery is spread out on the glass ; a small and very 

 thin cover-glass is placed over it, and the membrane is kept 

 moist with aqueous humour. The circulation in the 

 mesentery is extremely beautiful ; for the vessels are only 

 covered by a layer of very transparent epithelial scales. 



1 6 8. Tail of the Tadpole. The circulation may be 

 readily studied in the tadpole's tail. It is only necessary 

 to lay the animal on a slide in a drop of water under a 

 cover-glass. The tadpole is apt to move, however, and 

 therefore it is advantageous to give curara by putting the 

 animal in a watch-glassful of water containing two or three 

 minims of the curara solution ( 166). It is removed to a 

 slide and covered as before when the palsy is complete. 

 The phenomena of the circulation are similar to those 

 already described in the frog's web, but there is this im- 

 portant difference the diapedesis or emigration of the white 

 blood corpuscles through the walls of the capillaries and 

 small veins, so rarely seen in the frog's web or mesentery 

 unless inflammation be induced, is almost always to be seen 

 in the tadpole's tail under ordinary circumstances : but if a 



