Callous Tumour. 279 
and tumefied ; the external membrane was 
thickened, and theasperities of the fractured 
faces were removed by an effusion from the 
inner membrane. 
Exp. 4. Thirty-six hours after fracture — 
There was slight appearance of extravasa- 
tion ; the injured muscles were tumid and 
very vascular; the external membrane was 
thickened and vascular; a considerable effu- 
sion of coagulable lymph, evidently proceed- 
ing from the thickened external membrane, 
and also from the injured muscles, surrounded 
and enveloped the overwrapping portions of 
bone; the fractured faces of which were 
smoothed atid capped by effusion from the 
internal membrane, of a more compact and 
dense organization than the secondary effu- 
sion just noticed. 
From what has been stated, we have to no- 
tice the greater aptitude which exists in the 
internal membrane than in the external to 
the effusion of coagulable lymph; hence the 
one may be termed the primary, the other the 
secondary effusion. In the secondary effusion 
the capped surfaces of the fracture lie embed- 
ded ; the effusions do not run into each other, 
but present a distinct and observable diffe- 
rence ; this distinction evidently depends upon 
the difference in point of time, at which the 
