520 
PROFESSOR SIMONDS’ LECTURE. 
could only look at the effects that were produced; for if the air was 
impure, they had no means of discovering its impure particles. The 
potatoe disease had puzzled the greatest of English philosophers; 
but its cause and the laws which governed it were alike unknown. 
The perfume of a bouquet was acknowledged by all to be de¬ 
lightful to the sense of smell; but not a particle of that perfume 
could be detected by the chemist. Malaria was caused by the 
sun’s rays reflected on marshes and stagnant waters; but the 
deleterious matter which caused death could not be detected by the 
chemist if he were to analyse the air. Whether the disease de¬ 
pended on the altered condition of the air, or whether it was 
occasioned by some deleterious matter emanating from animal or 
vegetable decomposition, he could not say. It might be by one or 
both of these causes. The atmosphere might become impregnated 
with that which was injurious to life, and it was well known that 
many and great variations took place in it. It was a remarkable 
fact, that Dr. Prout found, on the 9th of February, 1832, there was 
a considerable difference in the weight of the air. The Lecturer 
then directed the attention of his hearers to the Bridgewater 
Treatise, in which that subject was fully treated upon. Dr. Prout 
said the weight of the air continued heavier than usual for several 
days, and was succeeded by cholera. He attributed it to some 
gases having caused the lower stratum of the air to be displaced. 
The wind turned from the west to the east, and remained there 
until the end of February, and the cholera commenced immediately 
after the change of the wind. He (the Lecturer) did not know 
whether the same thing had been observed with regard to the 
present visitation of this disease; but it would be quite sufficient 
for him to observe, that there was some cause at that time for the 
disturbance in the atmosphere which altered the weight of the air, 
and which might have caused the cholera. 
Whether pleuro-pneumonia was a disease depending on ordinary 
infection was a matter of some importance, because it would shew 
them that they should avoid purchasing cattle that were affected 
with the disease, or putting them amongst sound animals. It was 
true that in some cases they could trace the disease to some infected 
animal; but it was also true that animals had been attacked with it 
when no diseased ones had been in the neighbourhood. The attack 
might also be facilitated from an alteration in the food, or bad 
ventilation of the building in which the cattle stood. It might also 
arise from the excitement caused by their being conveyed from one 
part of the country to another, which rendered them more liable to 
be acted on by the specific cause of the disease. Care also should 
be taken not to feed the animals on that kind of food which appa¬ 
rently predisposed them to the attack. The question arose, How a 
deleterious atmosphere could produce such injurious effects'! He 
