2322 Journal of Applied Microscopy 



enough away from the body to permit the webs to be spread by separating the 

 toes as widely as possible without tearing the webs. The bottom of the frog's foot 

 adheres to the glass and keeps the webs stretched without the necessity of tying 

 or pinning. By moving the glass plate any one of the webs may be brought 

 under the objective. In using low power objectives the web needs no cover, 

 but for objectives of short working distance a bit of cover-glass, or a thin scale 

 of clear mica, should be placed on the web to protect the objective. 



It is sometimes desirable to reduce the rate of the flow of the blood in the 

 capillaries or to reverse its direction. To check the flow, press upon the thigh 

 with a small cylinder, e. g., the handle of a dissecting needle. To reverse the 

 current in the capillaries, roll the cylinder along the thigh toward the foot while 

 pressure is maintained. 



If the frog is kept under observation until its webs and body become dry, 

 the web should be moistened with a drop of water and a moist cloth spread over 

 the frog's body. To revive the frog after completing the study, place it in a 

 loosely covered tray or jar in shallow water, which will keep the animal's legs 

 and ventral side moist, but will not cover its mouth and nostrils. 



Tadpoles. — When these animals can be obtained, they are useful for studies 

 of the circulation of the blood and the morphological changes which occur dur- 

 ing metamorphosis. They are easily anesthetized by being placed in water five 

 parts, 1 per cent, chloretone one part, and they become passive in from three to 

 five minutes. To mount them for the study of the circulation of the blood with 

 the microscope, they are placed either in a watch glass with a small amount of 

 the anesthetizing solution, or on a glass plate in a pool of the solution. To 

 study the tadpole's mouth, turn it on its back in a watch glass. If small and 

 reasonably transparent specimens are selected and direct sunlight is reflected 

 by the mirror through a diaphragm of smaller diameter than the width of the 

 tadpole's body, it is possible to observe the pulsations of its heart. 



Large tadpoles are the best animals in which to demonstrate the circulation 

 of the blood by projection on a screen without a compound microscope. For 

 this purpose a " quarter size " projection lens is used with a very powerful oxy- 

 hydrogen, electric arc, or solar light. The tadpole is placed in anesthetizing 

 solution in a zoophyte trough, or in any glass cell with polished plate glass front. 

 The screen should be placed at twenty-five feet, or more, from the lantern so as 

 to obtain as large a magnification as the available light will permit. Under 

 favorable conditions, when the animal, mounted as above described, is placed 

 in the lantern at the position regularly occupied by a lantern slide and carefully 

 focussed, the arteries, veins and larger capillaries of the tail may be seen and the 

 corpuscles in the blood appear as small granules which can be seen at only a 

 few feet from the screen. The much more satisfactory projection with the com- 

 pound microscope will be described in a later article. 

 University of Chicago. A. H. CoLE. 



