30 PRACTICAL HISTOLOGY. 



certain conditions they at least, their constituent 

 granules may, as we shall presently see, exhibit 

 indications of vitality, yet nothing resemhling in 

 nature the amoeboid movements of the white blood- 

 corpuscles is ever observed in them. 



Finally, a few excessively fine and delicate threads 

 of fibrin may be observed stretching in different di- 

 rections across the field of the microscope ; but to *see 

 these distinctly a very high power is needed. 



Preparation 2. In order properly to study the 

 vital phenomena which are displayed by the white 

 blood-corpuscles, it is necessary, in the case of man 

 and warm-blooded animals, to maintain the drop of 

 blood under observation at or near the temperature 

 of the body. For this purpose we employ what is 

 known as a warm stage, of which there are several 

 forms in use. The simplest consists merely of an 

 oblong copper plate (Fig. 6), two inches by one inch, 

 from one side of which a rod of the same metal, four 

 or five inches long, projects. This plate has a round 



Fig. 6. 



Simple warm stage, with preparation upon it enclosed between two 

 cover-glasses. 



aperture in the middle, half an inch in diameter, 

 and is fastened to an ordinary slide by sealingwax. 

 The preparation is made as follows: Take first a 

 clean, large-sized (one inch square) cover-glass, which 

 in this case is to be used instead of a slide, and on it 

 place a small drop of salt solution. With this mix 



