OP THE MICROSCOPE. 103 



thread. The object is placed in the concavity, covered with a 

 piece of thin glass, and the end of the thread is carried under 

 the cover by means of a small notch cut in the slide with a 

 file. The bottle must be filled with very pure water, otherwise 

 the salts, etc., contained in it, become concentrated under the 

 thin cover, owing to the evaporation, and destroy the object. 



Frog Plate. The circulation of the blood in the capillaries 

 of living animals may be observed in the web of the frog's foot, 

 the tail of a small fish or water-lizard, the larvae of many insects, 

 the ear of a young mouse and the wing of the bat. The tongue 

 of the frog is also a favorite subject with some, and dissections 

 of the living animal have also been made, and the circulation ob- 

 served in the parts thus displayed. Except, however, for im- 

 portant investigations, we have no right thus to inflict torture 

 and destroy life, and, moreover, the obvious cruelty of the 

 means employed, will to most minds destroy nearly all the pleas- 

 ure arising from the beauty of the exhibition. Fortunately the 

 circulation of the blood in the foot of the frog may be witnessed 

 without subjecting the animal to any pain. For this purpose 

 the web of the hind foot is spread out over a piece of glass, 

 which is held in a frog-plate, as it is called, to which the little 

 animal is attached. The frog-plates usually sold, however, do 

 not lie conveniently on the stage of a small microscope; they 

 are apt to tip up, and there is no means of attaching them 

 firmly to the stage, so that it is impossible to incline the mi- 

 croscope. The annexed engravings represent a frog-plate, in 

 which these difficulties are avoided. As seen in the figure, it is 

 of the usual form, and has a large opening, into which is 

 burnished a piece of thinnish plate glass upon which the web 

 of the foot is laid. Around this opening is bored a number of 

 small holes, through which threads, tied to the frog's toes, are 

 passed and held firmly by small wooden pins. A series of holes 

 are also bored on each side and cut out at the edge, so that it is 

 unnecessary to pass the twine through the holes, as it may be 

 readily slipped into them. The frog may be enclosed in a bag, 

 one foot being left out, but a simpler and better plan is to 

 swathe him in a strip of muslin two inches wide and eight to 

 twelve inches long. The muslin is dipped in water, and the 



