26 PRACTICAL HISTOLOGY. 



slide (Fig. 5). When the lower blade of the forceps 

 nearly touches the slide, withdraw the instrument 

 carefully, so that the cover-glass may now rest evenly 

 upon the slide by its whole under surface, with the 

 blood in a uniform thin layer between. It is impor- 

 tant not to let the cover-glass down too suddenly, 

 for if dropped carelessly on the slide, many of the 

 corpuscles will be broken arid destroyed. When the 

 cover-glass is in its place, there ought to be just 

 enough blood entirely to fill the space between the 

 two glasses ; but it is better to have too little than 

 too much. It might be supposed that the delicate 

 corpuscles would be crushed between the cover-glass 

 and slide, but they are for the most part protected 

 from this by the buoying up of the cover-glass by 

 the liquid in which they float. 



The preparation made, it is to be at once trans- 

 ferred to the stage of the microscope, and examined 

 with a power of about BOO diameters. The Held of 

 the microscope will be seen crowded with corpus- 

 cles floating in a clear liquid. Probably the first 

 thing which will strike the beginner is the very faint 

 color which the so-called red corpuscles present, and 

 these will also most likely be the only kind of cor- 

 puscle that he will at first be able to distinguish. 

 But if at the moment 'of observation there happens- 

 to be a current in the fluid produced either acci- 

 dentally by a shaking of the room, or a draught of 

 air, or purposely by gently touching the cover-glass 

 with a bristle it will be seen that while most of 

 the corpuscles are carried along by the current, two 

 or three remain sticking to the glass, whilst the 

 others are carried past them; and, on close exami- 

 nation, it will further be clear that these are of a 

 different nature from the rest, being entirely devoid 

 of color, and of a pale granular appearance. They 

 are, in fact, white corpuscles, and once seen, will be 

 easily recognized again, even when the fluid is at a 

 standstill. 



Another thing that will be made manifest by tiny 



