MIDLAND COUNTIES VETERINARY MEDICAL ASSOCIATION. 771 
unless you want to lose all your cows, you must keep this one by 
herself for the next three months.” It was with difficulty that I 
ultimately ruled ; the cow was isolated for three months, at the end 
of which time she was turned with the others, the whole having 
remained free from contagious pleuro-pneumonia ever since. Thus 
from positive and negative evidence I have been led to consider that 
the minimum period of infection is the stage of incubation or period 
of incrementation of the morbific matter received by the infected 
animal ; and that the maximum period of infection is after the true 
character and consequences of the disease have been developed 
within an animal whose vis vitce has not succumbed to its ravages, 
and where nature has commenced to make the products of the 
affection excrementary. I therefore divide them into the incre- 
mentery and excrementary periods or stages of the disease, and I 
feel as if I could not lay sufficient stress upon this distinction, in 
the physio-pathological considerations of this virulently contagious 
malady. 
In concluding this part of our subject, I must appeal to the 
experience of every individual present, which when viewed in the 
light I have suggested will furnish fresh testimony as to the cause 
of the spread of this epizooty. It may be difficult to understand 
in what form the virus is transmitted, or of what it consists, 
yet my experience points to a fact, viz., that association and coha- 
bitation of healthy stock with those that are recovering from mild 
or severe attacks, or those which have passed however slightly the 
incrementary (incubative) period, and are therefore beginning to 
excrete the products of this disease, are necessary for the transmission 
of contagious pleuro-pneumonia. 
In the recent researches of Professor Tyndall on the decom- 
position of vapours by light, he has demonstrated that the dust 
particles constantly floating in our atmosphere are organic com- 
bustible matter. He says “ I was by no means prepared for this, 
for 1 had thought with the rest of the world that the dust of our 
air was in great part inorganic noncombustible ” (see Lecture 
delivered at the Royal Institution, January, 1870), and from it he 
infers a most beautiful germ theory of epidemic disease. 
As veterinary surgeons we are all aware and have no doubt 
frequently observed the large amount of dandriff, scurf, cuticular 
eruption given off from the skins of animals (especially have I seen 
it in the cow) when recovering from attacks of exanthematous disease. 
It is therefore comparatively easy to understand how this skin-dust, 
this exanthematous epithelial-debris, being organic matter, may and 
does float in the atmosphere that surrounds diseased animals, and 
may thus by inhalation be the means by which the germs of disease 
are implanted in the systems of others. However, gentlemen, this 
beautiful theory is worthy of your consideration. 
Symptoms . — Since the time of the Cattle Plague we have had 
placed in our thoughts and some of us in our hands a simple and 
precise method of medical research which we cannot value too 
highly — I mean the thermometer, thanks to Professor Gamgee. Of 
