2 Sir Everard Home on the conversion of Pus 
characteristic mark of distinction between the one and the 
other. 
As pus, in its first formation, has the appearance of being 
a transparent fluid in which globules afterwards are formed, 
whether the transparent fluid remains on the sore, or is re- 
moved to any other surface, as was proved by experiments 
made in the year 1788, and since that time laid before the 
public in my work upon Ulcers ; in this respect, pus might be 
considered to differ from blood ; but the following observa- 
tions, made by Mr. Bauer, tend to prove that a similar for- 
mation of globules is met with in the serum of blood. I 
shall give the remarks in his own words : “ That the glo- 
bules in the blood are produced in the serum, I first observed 
in July 1817, when I examined a small portion of human 
blood on a glass plate, to ascertain the real shape and size of 
the globules. I then found in one square of the micrometer 
(which was the 160,000 part of a square inch) two of these 
globules which were separated to a considerable distance 
from the rest ; they were entirely disengaged from the co- 
louring substance, and lay in pure clear serum, which co- 
vered the whole surface of the square of the micrometer. 
Having placed this particular square immediately under the 
focus of the microscope, I attentively examined the globules 
for about six or eight minutes, when I perceived two ex- 
tremely minute opaque spots arising in the clear serum within 
the same square of the micrometer, and which seemed in- 
creasing in size. In a few minutes longer, I perceived five 
or six more such opaque spots arising, and gradually in- 
creasing, and assuming the same form and appearance as 
the two original globules ; but the moisture of the serum 
