MEDICAL WORK WITH MICROSCOPE 



from various animals, the white corpuscles are 

 remarkably constant, measuring about 1/3000 inch 

 in warm-blooded animals and 1/2500 inch in rep- 

 tiles. Sometimes, as we are examining the white 

 blood corpuscles under the microscope, we shall 

 notice that they behave in a similar manner to the 

 Proteus Animalcule, which we described in our 

 chapter on Pond Life. A kind of creeping motion 

 takes place and the corpuscle loses its circular shape. 

 In our own blood this movement lasts but a very 

 few moments, in frogs' blood, by keeping our slide 

 moderately warm, we may witness the movement 

 for some time. 



It is perfectly easy to watch the circulation of 

 blood in the foot of a frog. For this purpose we 

 require a piece of apparatus known as a frog plate, 

 this is merely a flat brass plate perforated with 

 a number of holes, through which tape is passed 

 to bind the frog down and having also a hole the 

 size of the opening in the microscope stage, into 

 which a circle of glass is usually fitted. Such a plate 

 may be made of wood and will serve our purpose 

 quite as well as the more expensive brass plate. 

 We must bind our frog firmly, but not too tightly 

 with wet rag, leaving one leg exposed. This free 

 leg must now be fastened in such a manner that 

 one of the webs between its toes comes over the 

 opening in the plate, finally the toes must be care- 

 fully tied with string so that they remain apart and 

 the web is fully expanded. Having fixed our frog 

 in a satisfactory position let us examine his blood- 



171 



