RELATING TO CONTAGIOUS DISEASES. 635 
fourth of the acid. He then took a rabbit and held its nose 
to the mouth of the glass vessel, so that it was fully exposed 
to the vapour rising from the mixture. The animal became 
convulsed, and in a few seconds died. In this case, the blood 
of the rabbit became impregnated with the gas of the acid, 
without the pulmonary vessels being involved. The lungs 
are constituted of a myriad of tubes, whose membranous 
walls being extremely thin and porous, have the property of 
being permeable to vapour. The vapours arising from the 
blood in the same manner pass out, constituting the pulmo¬ 
nary transpiration. This may be plainly seen by introducing 
phosphorous into the blood. As soon as the blood contain¬ 
ing it arrives at the lungs, it escapes by respiration, the 
animal breathing opaque white vapours, consisting of phos¬ 
phorous acid, which inflame in contact with air. This con¬ 
tinual evaporation is no hinderance to the air coming in con¬ 
tact with the blood circulating through the pulmonary 
capillary vessels. What is without may pass into the blood, 
and vice versa . 
These phenomena command the utmost attention from 
medical men. It is of the greatest importance to know the 
composition of the air we respire, since so many diseases 
are in this manner produced. And though we with diffi¬ 
culty arrive at any certain knowledge of the miasms rising 
in marshy grounds, from the decomposition of putrid vege¬ 
table and animal matters. There can be no doubt whatever 
of their entering into the blood through the medium of the 
air, and so producing grave disease. In some countries 
especially such affections rage with extreme intensity ; in hot 
humid climates, and particularly on the sea-coast and borders 
of certain rivers, as for instance the Gulf of Mexico, Yera 
Cruz, New Orleans, &c. Such causes of disease admit of 
demonstration; since, by introduction of them into the blood, 
experimentally, may be produced, though not* exactly the 
yellow fever, symptoms bearing the greatest resemblance to it, 
with black vomit and speedy death. Lower Egypt, where 
the plague formerly prevailed so alarmingly, owing to such 
causes, has been rendered comparatively rare by the improved 
condition of the country. 
What we observe in such insalubrious countries and situ¬ 
ations abroad as these, is apt but too often to present itself 
in our dissecting-rooms at home. In spite of every pre¬ 
caution to disinfect such places, and retard the putrefaction 
of the bodies in them, every year we have a certain number 
of dissecting pupils seized with the low fever, called at the 
present day typhoid. 
