SiGERSoN — On the Atmosphere, 
19 
The acarus sucked into the air- passage would probably do no more than 
plug it up, whilst causing by the action of its claws a certain additional 
amount of irritation. 
On the other hand, knowing, as we do, of the growth of fungi in 
the mouth, and fauces, as well as upon the skin, it is to be feared that 
their being taken into the air-vessels of the lungs would not deprive 
them of vitality. Their growth there should cause as much disturbance 
as in the mouth ; but, on the other hand, they are less apt to send their 
mycelium into the lung, on account of the presence of ciliated epithe- 
lium. In cases where they have proved inoffensive, this has kept 
them off; then wrapt in mucus, they are coughed out. But there is no 
proof that they must be always inoffensive, though their agency has 
been as yet ignored. By spores in the air certain skin diseases may be 
propagated ; whilst the presence of an acarus in the atmosphere shows 
how another member of the Arachnida class, Sarcoptes scahiei, may be 
carried about to propagate the itch, which in northern parts of the 
country used to be a not unfrequent burrowing visitant on the exposed 
hands. Perhaps this disorder is more usually spread by the egg. Now, 
the acarus described, if it entered the lungs, might simply cause me- 
chanical occlusion, with some irritation superadded by the action of its 
claws. Dead, its decaying body might cause injury. But it is possible 
that it might live to produce its germs ; the larvae might survive long 
enough to cause much irritation. If a Sar copies were in- drawn, it 
would probably attempt to burrow immediately, as it does on the skin. 
Although some affections of the human lungs may probably be thus 
caused, it is obvious that the lower animals are far more likely to draw 
into their lungs these or similar injurious objects. The germs of para- 
sites that will make their way into the system may thus obtain an 
entrance. 
City Air. — Two Plates have been devoted to the objects discovered 
in the atmosphere of cities and crowds. One, with dark background, 
is an accurate transcript of four photomicrograms, which were selected 
from amongst several which I had taken when intending to use photo- 
graphy. It was abandoned for the pencil, as this was found more 
convenient, and apter to bring out more accurately the minuter objects 
and their internal anatomy. 
Ordinary dust, being chaotic, was disregarded in making the draw- 
ings. Generally speaking, it is formed by the wearing away of tha 
earth, and all things that on it are. In composition it varies with the 
locality. In the country the wind sweeps the roads and fields, and 
forms its dust of powdered clay and stone, some fine spicula of quartz, 
triturated fragments of excrementitious matter, rare and minute par- 
ticles of the hair and wool of animals worn off. In towns, dust simi- 
larly is found, but particles of soot are frequent. Pouchet has found them 
in the lungs of city birds, together with starch granules, which I have 
never encountered. In manufacturing towns, like Belfast, a fine soot-dust 
falls plentifully. In the factory districts of England it falls in un- 
welcome abundance. The amount of carbon thus sent into the air 
