Pollock,, on Granulated'^ Blood-discs. 5 
varying from a few minutes to perhaps an hour. At^ or 
perhaps rather before^ the time when the granulated appear- 
ance is most distinct, minute holes may be observed in the 
extreme ends of the tubercles where they are thinnest. These 
holes gradually increase in size while the entire disc grows 
less. The membrane is so thin at the point, and the holes 
are at first so minute, that it is requisite to use a good object- 
glass to make them out satisfactorily ; a superior fifth will do, 
but an eighth is better for the purpose. 
After the lapse of some hours cracks begin to appear in the 
thicker part of the membrane between the tubercles, which 
gradually increase in width, till ultimately the disc separates 
into several pieces. If a little spirit of wine be added to the 
blood the entire change appears to take place instantaneously. 
Not a disc in any sliape is to be seen, but there remains an 
abundance of extremely minute particles of no definite shape, 
apparently the debris of the former discs. These little 
particles I have frequently seen in recently drawn blood, 
which has been carefully preserved from all external con- 
tamination; and, indeed, I have frequently seen them in 
actual circulation in the living body, as I shall presently 
have occasion to mention. 
The addition of mineral acids causes the discs to shrink 
up, and renders their outlines darker. Hydrochloric acid, 
especially when diluted, produces in many of the discs a dis- 
position to adhere together, which gives to each disc a sort of 
double caudate shape, like two peas joined by their larger 
ends ; they are attached to one another by the smaller ends, 
and on separation resume their circular form. Nitric acid 
produces a sort of riddled appearance in the discs, which 
become full of small holes, and also appear to have the out- 
line eaten away in places. Liquor ammonise of ordinary 
strength dissolves the discs entirely, and they disappear at 
once. Those discs which are connected together in the form 
of rouleaux are much less disposed to undergo the change 
which I have described than those which are separate. 
I have always been anxious to discover whether any change 
of this description takes place while the blood is alive in the 
hody, which, for several reasons, I at first thought not 
unlikely, especially because, upon examining the blood, as 
quickly as it is possible to do after being drawn from the 
body, I have commonly found granulated discs in very 
difi'erent stages, some much more forward than others, 
looking as if the change in the latter had commenced before 
the blood was drawn. If the blood-discs, while in the body, 
did undergo a change in any degree similar to that I have 
