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them not only in septic, but in all contagious fluids, while 
Béchamp imagines that they form part of healthy structures. 
To determine these questions it was necessary (1) to subject 
the media to the action of some qualitative test by which 
the presence of the germinal matter of microzymes could be 
detected ; and (2) to make experiments in which their action 
on the animal liquids and. tissues would be observed under 
conditions similar to those which exist in the living body. 
As a test for the presence of microzyme germs we have used 
first, Pasteur’s solution, and secondly animal fluids, either 
‘diluted with pure water or undiluted. These liquids were 
selected on the ground first that they contain nitrogen, in 
the one case in the form of an ammonia salt, in the other in 
that of an albuminous compound, and secondly that although 
transparent and free from visible particles, when fresh, they 
become in a short time peopled with microzymes when kept 
under ordinary circumstances and at ordinary temperatures. 
Before using them, however, for the purpose intended, it was 
necessary to determine that they do not in themselves con- 
tain the conditions of evolution; in other words, that they 
can be prepared and kept in a state of absolute barrenness 
without prejudice to those qualities by which they are fitted 
to be employed as tests. These requirements could only be 
satisfied by a preliminary series of experiments having for 
their purpose to determine the question of so-called “ spon- 
taneous generation,” not in general, but with respect to the 
particular liquids to be used. In approaching a question of 
such difficulty, even with the limitation above stated, there 
are two methods of inquiry which suggest themselves; one 
consists in the comparison of results obtained when the cause 
to be investigated is present, with those which are produced 
when it is absent, all other conditions remaining unaltered 
(method of crucial experiment); the other in the comparison 
of variations in the results with variations in the circum- 
stances that lead to them (method of concomitant variations). 
We shall find that the first of these methods, which is clearly 
the most conclusive, is as applicable as the other to the 
particular question before us, that of the spontaneous evolu- 
tion of organic forms in any given medium. But even if it 
had not been so, the other method would still have been open 
to us, for if it could be shown that the appearance of micro- 
zymes in a given liquid is either delayed or diminished, in a 
degree proportionate to the degree of exposure to external 
influences, it might be safely inferred that exposure to the 
air is the efficient cause of their development. In the present 
instance it is possible to exclude all conceivable sources of 
