20 Proceedings of the Royal Irish Academy. 
and breathed by the lungs may help to account for the pallid fea- 
tures, the carbonaceous countenances, so to speak, of the inhabitants of 
towns. The inhabitants of the country, or of small non-manufacturing 
towns, are more frequently seen with ruddy cheeks. Besides this, 
there was the dust arising from the wearing away of clothes and cloths of 
all kinds; of vegetable and animal hairs, and products ground off fine 
by every movement ; of carpets, of furniture, and in libraries of books. 
Currents of air on walls and ceiling disintegrate and deprive them 
of particles ; and into the dust of rooms we carry, on clothes and boots, 
some of the dust from out of doors, whilst an open window may let in 
a large quantity. 
The characteristic special dust is what has been represented. In 
cities and crowds the motes are found to be frequently moist. Let us 
take first the photomicogram (Plate VI.). 
Figures 2, 3, and 4 show the objects which were received on glass, 
at breathing level, on traversing streets and cattle shows. The plan 
adopted was simple — to don a pair of spectacles ; and by this means 
motes were readily received from the atmosphere, in the most fre- 
quented places, without attracting undesirable notice. The vertical 
position of the glasses appears to count for little, as even a tolerable 
amount of dry dust adheres. When it was wished to search for what 
might have escaped the dry glass, a little glycerine was brushed over 
a portion of the glass, so as not to obscure the sight. 
The dumb-bell shapes that appear in figs. 2, 3, and 4, are frequently 
found. A globule of mucus sent rapidly forth into the air, gyrating, 
tends to draw asunder, and to divide in twain. Before this is accom- 
plished, the two separating globules are retained by a narrow isthmus 
that gradually becomes less, till it breaks. IN'umerous cavities, where 
air-bubbles existed, are seen in the dumb-bell mucus of fig. 2. In 
fig. 1 the rounder extremity of this dumb-bell is shown more largely 
magnified. Arborescent formations may be remarked, commencing 
here to display themselves ; but they will be shown more perfectly de- 
veloped upon another Plate. 
The presence of numbers of minute objects in the air, very plainly 
shown in these figures, must not, however, mislead the observer to 
imagine that the atmosphere contains them in an equal space so abun- 
dantly. The quality, rather than the quantity of the motes in the air, 
is the subject of investigation. 
It is to be remarked that some of the objects in fig. 3 might sug- 
gest to a casual investigator the idea that he had before him corpses 
of animalcules, and this would be an error. 
City Air (Plate YII). — It is necessary to state, at the outset, that all 
the objects depicted here are not as when first deposited. For instance, 
if we look at figs. 1 and 7, we see that they are adorned with beauti- 
ful branchy formations in their interiors. These were not detected 
without some study. When first deposited upon the glass, these 
objects were but homogeneous mucus : if left too long, the exquisite 
shapes may not be detected at all, as after they are formed they have no 
