52 JOURNAL OF SCIENCE 
The family relations of Bacteria are thus a little peculiar: 
each individual is half of its parent and moves itself by two cilia, 
one of which is a new structure, while the other is the identical 
instrument with which its immediate progenitor propelled itself 
through the ambient medium. Each one, again, in becoming a 
parent produces twins, and in so doing ceases to exist as a 
separate individual—losing itself wholly and literally in its off- 
spring. It will be seen from this that Bacteria multiply in 
geometrical progression, I-2-4-8-16, etc., as long as no check is 
put upon this increase. 
Let us now consider the actual relation existing between the 
presence of Bacteria in an organic liquid and its putrefaction. 
The subject will be made clearer if we consider first a simpler 
case in which the presence of a rapidly multiplying organism 
produces a change in the composition of a fluid—I mean the 
case of alcoholic fermentation which is brought about by the 
microscopic yeast-plant or Saccharomyces cerevisiae. 
Each yeast-plant may be compared to an ‘inactive globular 
Bacterium of great size, since it is no less than one two-thousand 
five-hundredth to one-three-thousandth of an inch in diameter. 
Like Bacterium it consists of protoplasm surrounded by a wall 
of cellulose. It multiplies very rapidly by sending off little buds 
which become detatched and grow to the size of the parent cell. 
_ In Alcoholic fermentation yeast is added to some saccharine 
fluid—such as the “sweetwort” or infusion of malt used in the 
preparation of beer. Sugar consists of a certain number of atoms 
of carbon, oxygen, and hydrogen combined in certain definite 
proportions ; through the agency of the yeast-plant oxygen is 
withdrawn from it and it thereupon becomes split up into 
substances entirely different from sugar, one of which—alcohol 
—remains in the fluid, while the other—carbonic acid—is given 
off as a heavy suffocating gas. We may picture to ourselves the 
atoms of sugar piled up like a house of cards, and then imagine 
the yeast pulling away the bottom card, when of course the whole 
pile will fall down. 
A very similar process takes place in organic infusions under 
the influence of Bacteria : the latter withdraw certain constituents 
from the substances contained in the infusion ; the substances 
are then decomposed, being split up into new compounds, 
amongst which are the various evil-smelling gases to which the 
odour of putrefaction is due. 
In order that Bacteria should live and multiply, they must 
be provided with a constant supply of these decomposable 
substances. Buta vessel of hay-infusion or other suitable fluid 
contains only a limited supply, therefore as soon as this is ex- 
hausted, the Bacteria must come to anend. This is in fact what 
happens when the fluid clears after putrefaction is properly over : 
the Bacteria have completed the process of splitting up the con- 
tituents of the fluid, the evolution of stinking gases ceases, and 
the Bacteria having no more food left die and disappear. 
