118 Transactions of the Royal Microscopical Society. 
action of water ; but, on the contrary, with the exception of a very 
slight diminution in size, they preserve the exact form, whether 
normal or distorted, which they possessed before the application of 
the water. Nevertheless, if the water be applied immediately after 
the various changes of form have taken place, they resume their 
original shape, as I have observed. 
The presence of a delicate membraneous layer may be further- 
more demonstrated by a simple experiment on the fresh blood- 
corpuscles, and without the assistance of any reagent. I cannot 
forbear to recommend this experiment, particularly to those histolo- 
gists who deny the existence of this layer, in order to convince 
them of their error. It is as follows : — A very small drop of 
human blood, about the size of a small pin’s head, is taken and 
placed upon the glass slide. After being covered with a small 
round covering glass, this is firmly pressed down upon the blood 
by means of the point of a forceps, with the object of compress- 
ing or crushing the blood-corpuscles as far as possible. For this 
reason, the point of the instrument may be passed over the cover- 
ing glass, for the purpose of applying the pressure to every part 
of the blood ; or the blood may be rubbed between the two glasses 
until they adhere to each other. A subsequent microscopical 
examination will show that it is not an easy matter to crush these 
bodies into a homogeneous mass, though they may in some places, 
where they formed small masses, have apparently run into each 
other. In directing our attention to single individuals, we find 
that they have considerably increased in their dimensions by 
having been pressed perfectly flat. Every trace of their central 
concavities and peripheral convexities, indicated in their normal 
condition by their light centres and by their bright margins, has 
disappeared ; their bodies are uniform in colour or shaded through- 
out, with the exception of a light greenish border, similar or even 
more distinct than that seen on the coloured blood-corpuscles of 
the Amphiuma or Frog. On some of them clear streaks, repre- 
senting fissures, caused by a rupture of the membraneous layer 
are observed. Those blood-corpuscles which had assumed the 
mulberry or thorn-apple form before the pressure was applied, 
also will be found pressed perfectly flat, with their dimensions 
increased and their margins crenated. The same light greenish 
border, mentioned before, will also characterize in these instances 
the margins of the blood-corpuscles. Some corpuscles have pre- 
served their form of a circle, while the outlines of others appear 
more or less irregular, as kidney-shaped, ellipsoidal, spindle-formed, 
&c., in accordance with the form which they possessed before the 
application of the pressure ; or when pressed into a mass, accord- 
ing to the degree of the mutual pressure exerted upon each other. 
If now a group or small mass of blood-corpuscles in the prepara- 
