460 RESEARCHES INTO THE CAUSES OE BLINDNESS. 
then evaporating it in a gentle heat, after having poured in some 
drops of concentrated sulphuric acid. By these means we undoubt- 
edly obtain a blackish matter depositing carbon ; but the formation 
of wiry striata, and a dirty greyish hue, proved plainly enough 
that the vapour of the water held in suspension an organic matter 
easily rendered putrid by heat, and noxious to men and animals. 
Hence it results : — 1st. That a purulent ophthalmia was deve- 
loped in upwards of thirty horses of the detachment quartered at 
St. Avoid. 
2d. That it was caused by the miasmata exhaled from the 
banks of a little river running over a peaty bed, and situated not far 
from the barracks in a marshy spot. 
3d. That notwithstanding the gravity of the symptoms, in eight 
of them, the results of the treatment employed were most satis- 
factory. 
Army veterinary surgeons have this great advantage over their 
civil colleagues, that they have their patients constantly under their 
care, and can see them daily if they wish. Profiting thus by our 
position, we carefully watched the animals that had been affected, 
and were not a little surprised, after the lapse of nearly three 
months, to see that two of the horses that had apparently been 
perfectly cured were blind. Since that period four more have 
become similarly blemished ; thus, in the short space of one year, 
six out of the thirty horses attacked with ophthalmia lost their 
sight. 
On reviewing the contents of this chapter, it is, in our opinion, 
impossible not to be struck by the explanation which it affords on 
some previously inexplicable points. For example, it has been 
remarked that, in the south, scarcely any horses are attacked which 
remain out at grass, while in the north and east it is principally 
those who lose their sight. Does not this arise from the influ- 
ence of ambient matter, and especially from that fluid which pre- 
sides over the performance of vegetable and animal functions, and 
the modifications which these undergo under different atmospheric 
combinations 1 The cold, foggy, or damp air inhaled by horses in 
the north and east — the innutritious grasses, impregnated with 
moisture, which grow there — the damp, marshy nature of the soil 
whence miasmic matters are exhaled, mingled with watery vapour; 
all these combined influences are, as our researches have clearly 
proved, fully capable of producing blindness ; whereas the pure 
dry air of the south, and the fine luxuriant and nutritious grass 
which grows in this climate, act as preservatives against that 
affection. One remark, the truth of which we have personally 
observed, and which tends to the support of this opinion, is, that 
blindness is not so frequent in horses on the borders of the Sarre, 
