238 THE ORIGIN AND PEOPAGATION OF DISEASE. 



putrefaction. This lias a more immediate connection with pathology 

 than fermentation, because it is a change which takes place in animal 

 substances, while fermentation, at least in its simpler forms, relates 

 mainly to products of a vegetable origin. 



Putrefaction was formerly regarded as the natural and inevitable de- 

 composition of dead animal matter when exposed to the oxygen of 

 the atmospheric air. But in reality something else is necessary. In 

 every putrefying liquid there are a growth and development of minute 

 living organisms. If we take a clear solution of any nitrogenized ani- 

 mal or vegetable matter and expose it to the air at a moderate tempera- 

 ture, after a short time it becomes turbid. This turbidity is the first 

 evidence of commencing putrefaction, and it is exactly analogous to the 

 turbidity of a saccharine liquid which is beginning to ferment. Micro- 

 scopic examination shows that it is due to the presence of innumerable 

 ^ac^enitm-oells, g-o^oo ^f an inch long, by 40000 ^^ ^^ ii^ch wide, moving 

 in every direction, and multiplying by a rapid process of subdivision. 

 As long as putrefaction goes on, so long the Bacteria multiply. When 

 it comes to an end the liquid becomes clear, and there is a quiescent 

 layer of Bacteria deposited upon the bottom. The least particle of this 

 layer added to another albuminous Mquid will excite putrefaction in it, 

 and will produce a new development of Bacterium-Gells^ the quantity of 

 which is limited only by that of the albuminous matter which serves for 

 their nourishment and growth. 



'Now, Bacteria are the smallest and most obscure of living things 

 Their minute size alone is a sufficient obstacle, with our present micro- 

 scopes, to their complete and satisfactory study in all particulars. Never- 

 theless, some important facts have been established with regard to them. 

 In the first place, they are undoubtedly vegetable in their nature, and 

 consist of cells which multiply by division, not by budding. They 

 require for their growth a temperature between the limits of freezing 

 and boiling water. They consist of a protoplasmic matter, surrounded 

 by an envelope of vegetable cellulose. They live upon nitrogenized 

 and carbonaceous organic matters in solution, and, like other colorless 

 plants, absorb oxygen and exhale carbonic acid. They present a variety 

 of genera and species, which may be distinguished from each other with 

 some approach to accuracy ; and, of these. Bacterium termo is the most 

 constant and indispensable inhabitant of putrefying infusions. 



As to the true relations between bacteria and putrefaction, almost the 

 same course of inquiry has been followed as in the case of the yeast-fungus 

 and fermentation. At first regarded simply as an incidental accompani- 

 ment of the process, they are now considered as its essential and imme- 

 diate cause. This view is distinctly stated by Dr. Ferdinand Cohn, to 

 whom we owe more definite information on the natural history and mi- 

 croscopic characters of Bacteria than to any other observer. Dr. Oohn 

 is a professed scientific and experimental botanist, and director of the 

 Institute of Vegetable Physiology at Breslau. He was the first to 



