94 



EXPERIMENTAL PHYSIOLOGY 



glass disc in the manner shown in Fig. 76, with the mesentery resting 

 on the disc. The mesentery must be kept wet with Ringer's solution ; 

 it may be covered by a very thin cover-glass. A higher power can then 

 be used. 



3. In the tadpole's tail. To observe the flow of blood in this 

 structure all that is necessary is to immobilise a tadpole with water 

 shaken up with ether, and place it upon a glass slide in the same fluid. 

 The thin edges of the tail are observed with the microscope. 



4. In the toad's lung. This is prepared much in the same way as 

 the frog's mesentery. The lung is allowed to protrude from an aper- 



FIG. 76. Method of displaying frog's mesenterj^ for microscopic 

 observation (Ranvier). L, Glass or cork plate ; B, cork, with 

 cylindrical hole through it ; I, intestine ; M, mesentery. 



ture in the side of the thorax and to rest on the mesentery disc. 

 The toad is used in preference to the frog because its lung normally 

 remains distended with air, and requires no special appliance for 

 keeping it filled. 



5. In the toad's tongue. This is on the whole the best object for 

 the study of the capillary circulation in cold-blooded animals: the 

 frog's tongue is not quite as good. 



The animal is immobilised as before, and is laid on the frog-cork on 

 its back, with the end of the snout near the slot a. The lower jaw 

 is then raised, and the tongue, which is folded back in the mouth, 

 is drawn forward and fastened, with as little injury as possible, by fine 



