Animal Substances into a fatly Matter. 243 
a very beautiful pellicle, which is white in general ; sometimes 
it refracts the sun's rays, producing the prismatic colours. 
Fish may be also changed ; and I recollect having seen in 
some old author, whose name I cannot recollect, a passage in 
which he mentions a circumstance where something of this 
kind happened in a whale. He says, that after this fish has 
been putrifying on the shore some time, the people have a se- 
cret by which they can procure and purify lumps, which they 
find to be similar to the spermaceti which they get in the usual 
way. 
I have heard from many people, observations which they 
had made where this substance had been formed, and which 
they could not account for ; but as the circumstances were the 
same as those beforementioned, I shall forbear giving addi- 
tional trouble. 
On seeing a body opened some time ago, where there was 
a great collection of water in the cavity of the thorax, I ob- 
served that the surface of the lungs was covered with a whitish 
crust. I remarked to a friend, that I thought this crust was 
owing to some combinations which had taken place between 
the lungs or pleura and the serous fluid effused, similar to 
what I had observed between flesh and water ; or that the se- 
rous fluid had acted on the coagulable matter, and had pro- 
duced a similar change. 
Dr. Cleghorn mentions a circumstance, which in some 
measure seems to agree with the observation then made. As 
the fact is a curious one, I shall subjoin the following extract. 
He is speaking of abscesses formed in the lungs. “ These ab- 
“ scesses had sometimes emptied themselves into the cavity of 
“ the thorax, so that the lungs floated in purulent serum, their 
