32 
PEARLS IN A BULLOCK’S BLADDER. 
strong resemblance to pearls which these concretions occasionally 
possess. This singular fact is not noticed by Scharling, Vogel, or 
L’Heritier, nor can I find any description of them in the last edi¬ 
tion of Dr. Prout’s work on Renal Diseases. Dr. Bird appears to 
have met with them of very small size compared with those ex¬ 
amined in the present case, since he speaks of their appearance 
under the microscope. He says of them, “ These beautiful little 
bodies present a remarkable resemblance to pearls, the well-known 
concretions of the pearl-oyster. Indeed, they may almost be re¬ 
garded as urinary pearls.” 
I have since procured some of the oyster-pearls rejected by 
jewellers in consequence of their dark colour, and find them to be, 
in physical structure and chemical composition, identical with 
those taken from the bladder of the bullock. There is nothing 
surprising in this analogy, when it is considered that the oyster is 
partly composed of mucus similar to that of the mucous lining of 
the urinary bladder, and that the base, lime, is present in sea-water 
as well as in urine. Under some morbid condition of the system, 
the lime meets with carbonic acid; and, when the deposit takes 
place very slowly and uniformly around a centre, a sphere of car¬ 
bonate of lime, having a pearly lustre, may be thus formed in either 
case. Pearl consists of concentric layers of carbonate of lime in- 
terstratified with animal matter. When this is abundant, and of 
a dark colour, the pearl is rejected as unfit for ornamental purposes. 
Dr. Ure states that the oyster-pearl is formed under a disease 
caused by the introduction of foreign bodies within the shells. In 
making a careful examination of an oyster-pearl, I have found no 
foreign body : the whole consisted of carbonate of lime, the internal 
portion being of a brownish colour, and amorphous, while the ex¬ 
ternal portion was composed of thin concentric layers having the 
usual pearly lustre.— Med. Gaz. 
[Some appear to think that pearls are always produced by or 
from the internal surface of the shell, and it is stated that their 
formation may be promoted by mechanical irritation of that surface; 
but this must be a mistake, for the shell once formed is lifeless and 
incapable of growth or secretion. The pearls are formed in, on, or 
from, the tegumentary membrane of the animal. We have more 
than once seen them embedded in the soft parts in the oyster, be¬ 
neath or in its cutaneous or mucous covering, visible and projecting 
from the surface.— Ed. Dub. Med. Press.] 
