COLORLESS CORPUSCLES OF BLOOD. 601 



tinguished from the large nuclear mass which it incloses; by 

 treating the cell with water or acetic acid, however, the mem- 

 brane is distended, and the nucleus very commonly breaks up 

 into fragments in its interior. This last appearance seems natural 

 to the corpuscles in a more advanced condition ; and the isolated 

 particles are often to be seen executing an active molecular 

 movement within the cell, which continues when they are dis- 

 charged by the bursting of the cell, consequent upon the addition 

 of a solution of potass. These corpuscles are occasionally seen 

 to exhibit very curious changes of form, which remind us of those 

 of the Amoeba ( 261) ; a protrusion taking place from the same 

 portion of the cell-wall, the form of which seems quite indetermi- 

 nate ; and this being soon succeeded by another, from some dif- 

 ferent part of the cell, the first being either drawn in again, or 

 remaining as it was. These changes have been observed, not 

 only in the " colorless corpuscles" of the blood of various Verte- 

 brated animals, but also in the corpuscles floating in the circu- 

 lating fluid of the higher Invertebrata, such as the Crab, which 

 resemble the "colorless" corpuscles of Vertebrated blood rather 

 than its " red" corpuscles, these last, in fact, being altogether 

 peculiar to the circulating fluid of Vertebrated animals. 



416. In examining the Blood microscopically, it is, of course, 

 of importance to obtain as thin a stratum of it as possible, so 

 that the corpuscles may not overlie one another. This is best 

 accomplished by selecting a piece of thin glass of perfect flat- 

 ness, and then, having received a small drop of blood upon a 

 glass slide, to lay the thin glass, not upon this, but with its edge 

 just touching the edge of the drop ; for the blood will then be 

 drawn in by capillary attraction, so as to spread in a uniformly 

 thin layer between the two glasses. The inexperienced observer 

 will be surprised at the very pale hue which the red corpuscles 

 exhibit beneath the microscope, when seen in a single stratum; 

 but this surprise need no longer be felt, when it is borne in 

 mind that the thickness of the film of coloring fluid which they 

 contain, is probably not more than l-20,000th of an inch ; and if 

 a drop of ink, or of almost any colored liquid, however dark, be 

 pressed out between two glasses into an equally thin film, its hue 

 will be lightened in the same degree. The red hue of the 

 corpuscles, however, becomes . obvious enough, when two or 

 more layers of them are seen through at once. The " colorless 

 corpuscles" in Human blood are usually not more than 1-350 of 

 the " red," so that no more than one or two are likely to be in 

 the field at once ; and these may generally be recognized most 

 readily, by their standing apart from the rest ; for whilst the 

 "red" corpuscles have a tendency to adhere to each other by 

 their discoidal surfaces, the " colorless" show no such disposition. 

 Thin films of blood may be preserved in the liquid state, with 

 little change, by applying gold size or asphalte round the edge 

 of the thin glass cover before evaporation has had time to take 



