288 Observations upon the 
in the secondary effusion, which in a state of 
health ought to envelope the injury; upon 
examining externally, we therefore find no 
tumour, and the bone grates and is moveable 
upon the slightest pressure. This effusion, 
when natural, is copious, and when the sur- 
rounding soft parts are not too much injured, 
it is increased, and they become a powerful, 
though not necessary auxilliary to its forma- . 
tion; it serves early as a kind of natural li- 
gature, supporting the fracture and restrain- 
ing its motions. As the secondary effusion 
is always slight or totally absent in a diseased 
state of the external membrane, this shews 
that it owes its origin chiefly to that mem- 
brane; and the existence of the primary 
effusion capping the face of the fracture, 
even in a total failure of the secondary one, 
shews the distinct origin of the two; and 
that we can only attribute the primary effu- 
sion to the internal periosteum or membrane 
lining the canal of the bone. And these opi- 
nions will be confirmed by examining the ap- 
pearances of a fracture, when the internal 
membrane does not go through its assigned 
fanction at a time when the external performs 
its part regularly in the process of repa- 
ration. 
