28 HIRUDO. 
of such as are derived through the medium of fluids. Heat, together 
with the purity of the surrounding element, conjoined with hunger, 
form the principal stimulus to activity. Absolute torpor follows expo- 
sure to even moderate degrees of cold. Hence the secret, regarding 
which, reserve is sometimes practised—immersion of leeches in tepid 
water to facilitate their use on application. The size and vigour of all 
the tribe depend much on genial temperature, together with the frequent 
and copious renewal of their native element. Their survivance other- 
wise is only a testimony to the tenacity of life. Here, and in the greater 
and sudden atmospherical alternations, will be found the source of those 
barometrical demonstrations ascribed to the Medicinal Leech. These 
originate in its susceptibility of external impressions. 
Like the former, this animal has ten marginal specks or eyes, and 
these are generally so obscure,gthat it is difficult to find them. There is 
little besides that is remarkable in its appearance. Its size is very variable, 
those being considered full-grown which extend three, four, five, or six 
inches. Some are even larger. 
The Medicinal Leech is known to be indigenous in different parts 
of Scotland. I once received three from Lochleven, one of them a fine 
specimen, Plate II. fig. 11, which is represented rather above the na- 
tural dimensions. Two also reached me from Muthill, said to have been 
taken in Loch Fleury, described as on the summit of a hill near Blairn- 
lone, three miles south of Comrie, and six miles west of Crieff. A pool 
near the Loch of Menteith has been named as containing this animal, and 
also certain ponds belonging to John Burn Murdoch, Esq. of Gartincaber. 
A lady in the county of Fife, is the reputed owner of a pond containing 
Medicinal Leeches, which she reserves exclusively for the use of the 
poor. Likewise I have been told of a leech distinguished by yellow 
lines, but of more questionable identity, mhabiting Loch Turrit, about 
three miles west of Crieff. 
Besides the preceding, various other places have been named, though 
I do not repose much confidence in the species reported, without seeing 
specimens. 
The leeches from Muthill were very large. On carrying them to 
