184 Transactions.—Zoology. 
1 and 2 were very turbid, and both showed under the microscope numerous 
Bacteria, bu& No. 1 (the unboiled speeimen) showed in addition some free 
swimming Infusorians, derived (they or their spores) in all probability from 
the hay, but possibly from the water. The boiling of No. 2 had killed these 
higher organisms. No. 8 was still clear. After several months (it was in 
July that I put up these specimens, examine them now) Nos. 1 and 2 are 
positively filthy, they are far advanced in decomposition, and owing to 
evaporation are drying up. No. 8 has diminished fully half its bulk owing 
to the same cause ; but what remains is a clear fluid, and if we examine a 
drop of it under the microscope, I feel well assured will not show any living 
organisms. Now this is very remarkable. What is this exemption from 
decomposition and the associated development of organisms due to? It is 
not due to the previous destruction of organisms by boiling, else No. 2 would 
have escaped. Neither is it due to the exclusion of air, for air has been 
freely admitted; therefore we can only conclude that the exemption is owing 
to the cotton wool plug having caught and retained the germs which are 
ever present in the atmosphere. 
I have also a specimen of a small quantity of a highly putrescible animal 
fluid, which has remained clear and unaltered by means of the same simple 
precautions. 
We may here for a few minutes consider what is the nature of putrefac- 
lion; putrefaction expresses the chemical change which organic matter 
undergoes when exposed to air, dust, etc. If we take a solution of an 
inorganic salt such as nitrate of potash and set it on one side and examine 
it after a long interval, we should find it was nitrate of potash still; similarly 
if we take a number of neutral salts, taking care to select only those that 
would not chemically react on each other, we should still find that even after 
a very long time they would still be unaltered; but with an organic fluid 
the case would be different; a solution of albumen such as the serum of 
blood would very soon putrefy, that is, it would undergo a chemical change, 
and as this change is accompanied with an offensive smell, it is called putre- 
faction. The process is identical with fermentation, in fact only a variety, 
and fermentation is a chemical change induced in an organic fluid by means 
of the growth in that fluid of certain definite minute organisms; thus the 
alcoholic fermentation is caused by the yeast plant (Torula cerevisia) the 
batyric fermentation by the growth of Bacillus subtilis; this organism grows 
best where there is but very little oxygen, and I may state here in parenthesis 
that the well known but at the same time unpleasant symptom of heart- 
burn is caused by this particular fermentation; the lactic fermentation, or 
the souring of milk, by the Bacterium lactis, and the numerous fermentations 
and decompositions of organic fluids by the different species of Bacterium, 
