1 88 
Sir Everard Home's additions to 
lative size in the micrometer, which will give a correct result 
which ever mode of measurement is adopted respecting the 
original globule. 
To do away the objection which has been made to gas 
being contained in the net- work formed in coagulated blood, 
I first made the following experiment. I placed a vessel 
nearly filled with blood drawn from the arm, under the re- 
ceiver of an air pump, and by exhaustion extracted the gas 
contained in the blood. This blood deprived of its gas 
when coagulated, exhibited no appearance of net-work. 
In that part which had coagulated before the exhaustion was 
completed, the net-work was beautifully distinct. 
When blood is drawn from the arm into a cup, and allow- 
ed to stand 48 hours, the serum is separated, and every 
where encloses the coagulum. The greater part of the sur- 
face of the coagulum is covered with small round holes in 
which the gas had collected, and then forced its way out 
into the serum. But if blood taken by cupping is allowed to 
stand 48 hours in a cup, sometimes the serum is only separated 
in small quantity, and does not rise above the coagulum, in 
consequence of a film or pellicle forming on the surface of 
the coagulum, and fixing itself to the edge of the cup all 
round. This pellicle when examined at the end of 48 hours 
appears to contain ramifying vessels. This arises from the 
mode by which the blood is extracted depriving it of a part of 
its carbonic acid gas, and what remains is not sufficient in 
quantity to burst the pellicle, and when in the act of extrication 
it arrives immediately under the pellicle, it is forced to spread 
in different directions, putting on this appearance. 
Having ascertained that this appearance is produced by the 
