114 REPORT—1863. 
easily poisoned, except by corrosives, or by excess of stimulus to the roots—too 
much guano for instance ; delicate plants may be watered with a solution of mor- 
phia or of hydrocyanic acid with impunity. With respect to chemical impurities 
of the air, different plants have different susceptibilities for such influence, and the 
greater or less impurity of the atmosphere may, indeed, be shown from the effects 
on plants. Thus the rhododendron will flourish in an air fatal to the common 
laurel ; wheat will luxuriate when a holly or oak will die. Some plants which 
appear naturally to luxuriate in the coal strata—as the oak, holly, or some ferns— 
die when the mines begin to be worked. Fortunately, annuals suffer least; for 
instance, corn and wheat do well where nothing else can, and perhaps the exhala- 
tions in question may even tend to ripen them. An increasing deterioration of the 
atmosphere in towns and mining districts may be estimated by means of plants as 
follows:—1. In the smallest degree of impurity trees are destitute of the leafy 
lichens; and Ericz, the Scotch fir, and the larch die. 2. Next, the common lau- 
rel, the Deodara cedar, the Ivish arbutus, the laurestinus, and the yew die, 3. The 
araucaria, the thuja, the common cedar, the mezereon, and the Portugal laurel die. 
4, The common holly, the rhododendron, the oak, and the elm die. 5. Annuals 
still live, and the almond, poplar, and many roses thrive, fruit-trees are barren, 
eas unproductive. 6, Hieracia, Reseda lutea, the elder, some saxifrages and se- 
ums, with many syngenesious and cruciferous weeds still luxuriate. 
On a Parasitical Acarus of the Anodon. By R. Garner, F.L.S. 
The little Arachnoid in question inhabits the gills of the Anodon, and was fully 
described as the Atazx ypsilophora by Van Beneden. The author also worked out 
its history: the ova, deposited in the mantleof the mollusk; the larvee, with rostrum ; 
the eyes, at first four and then two in number; moulting, and till the last moult 
minus one pair of legs. The author attributes the formation of pearls par excellence 
to the presence of a distoma. Around these parasites, as nuclei, shelly matter is 
deposited, sometimes at first dark in colour, sometimes clear nacre from the com- 
mencement. Hence pearls may have a dark centre or not, or, if the dark deposit 
goes on, a black or purple pearl may be formed. It is sometimes impossible to dis- 
tinguish a distoma from an incipient pearl, except by pressure, when the pearl will 
burst; or polarized light will show the layer of shelly matter, or frequently the 
organization of the distoma may be seen through the nacreous covering. But other 
irritants may, exceptionally, the author admits, give rise to the formation of pearls 
or pearly prominences, as for instance the ova of parasites. Those of the Ataz, 
when they are deposited in the external layer of the mantle of the mollusk, produce 
numerous pearly prominences to be seen upon the interior surface of the shell to- 
wards the retral extremity, 
Further Observations on the Normal Position of the Epiglottis. 
By Georer D. Gres, W.D., MA., F.GS. 
When this subject was brought before the Association last year, it was the 
generally received opinion that the epiglottis in the healthy state was always erect 
and perpendicular. Its peculiar structure fayoured this view. The examination 
of 300 healthy persons, up to the month of October 1862, has shown the author 
that, in a certain percentage, the cartilage was in a semipendent, transverse, 
oblique, or nearly quite horizontal position. This was during passiye examination, 
independently of the act of swallowing, of phonation, or of any motion in the 
structures of the throat, and carefully observed when the tongue was protruded 
forward and held outside the mouth. Up to the present time, he had examined 
ag many as 680 persons, of various ages and sex, as or less in perfect health, 
or nearly approaching to it, and the percentage, curiously enough, remained the 
same—namely, eleven; that is, eleven persons out of every 100 individuals pos- 
sess an epiglottis whose position is not erect. This striking difference between an 
erect and a pendent epiglottis is a question of the highest importance in everything 
appertaining to voice and throat, whether in health or disease. The pendent con- 
dition of the epiglottis is sometimes congenital, and, when it occurs in the young, 
there is great danger to life during their passage through the diseases of child- 
