184 Transactions. — Zoology. 



1 and 2 were very turbid, and both showed under the microscope numerous 

 Bacteria, but No. 1 (the unboiled specimen) 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. 3 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. 3 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- 

 tion ; 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 caUed 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 cerevism) 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, 



