AN URINARY CALCULUS AND ITS EXPULSION. 743 
tough, and compressible, yet easily fractured, of organic 
origin, chars, decomposes, and disappears by the continued 
application of heat, leaving a very small trace of inorganic 
matter. This nucleus was in all probability a coagulum of 
blood. The component parts of the specimen are much more 
condensed in some places than in others ; for instance, that 
half considered to he the lower one, and resting on the floor 
of the bladder, has its particles more closely arranged, more 
condensed, than those of the upper or free half, where there 
are many small interstices, and which, unlike the lower half, 
is partially made up of a soft, smooth, chalky material, 
reducible to powder by slight pressure. The remainder 
(referring to the internal part) is of the gravelly nature. The 
difference seen to exist in these two characters is considered 
to be due to molecular arrangement, and not to their possess¬ 
ing different chemical compositions. 
The weight of the lower half very much exceeds that of 
the upper, and the nucleus is placed at a point nearer to the 
lower surface than to the upper one; in other respects it 
occupies a central position. 
From the contour of the exterior of the calculus, the dis¬ 
position of its interior, and the fact that its presence in the 
viscus had not caused any previous derangement, it is to be 
inferred that the foreign body maintained a stationary posi¬ 
tion, or that its degree of movement ^vas of a very limited 
extent. 
The containing organ had adapted itself to the gradual 
increase of the stone, the formation of which must have 
extended over a considerable period. 
Its displacement from the usual position it held no doubt 
gave rise to the symptoms described, and its ultimate expul¬ 
sion. Evidence is not furuished that would tend to account 
for a cause of its dislodgement, but it would be interesting 
to ascertain in what way the removal from its original site 
w^as effected. 
The size of the calculus has nothing particularly attached 
to it to recommend its detailed description; but this may be 
interesting, at least to a few. Viewing it as a body, offering 
immense resistance to the muscular contractions of the 
bladder, as one subject to no modification of form to render 
its expulsion easy, and considering the fact that so large a 
mass was expelled per urethram by the sole exertions of the 
mare, it does become a case of unusual interest, and is worthy 
of being placed on record. 
The results of a rough chemical analysis, and those of a 
microscopical examination, have afforded a general idea of 
