1878. ] 1 05 (Parker. 
a very serious error. My experiments demonstrate the fact that or- 
ganisms pass with facility through the finest filtering paper, and con- 
sequently are found in the deposits. Another very common source of 
error is the imperfect sealing of the flasks. Many flasks sealed with 
the spirit lamp and blow-pipe in the usual manner will, if inverted, 
show the imperfect sealing by the bubbles of air passing up through 
the liquid from an imperceptible aperture left in the sealing process. 
Still another common source of error is the belief that in a given in- 
fusion certain organisms will always appear in the same length of 
time. Sofar from this being the case,it is well known that an in- 
fusion will at one time, swarm with bacteria and other low forms of 
lifein a few hours; while, at another time, an infusion prepared in 
the same manner and surrounded, so far as can be seen, by the same 
conditions, may remain for a considerable time without any indication 
of life. The above are the mistakes most likely to occur with ex- 
perimenters in this field. The greatest care and attention are neces- 
sary to avoid them, the subject being beset with difficulties on every 
hand. The exaggerated statements respecting organisms apparent in 
flasks supposed to be hermetically sealed, and heated to the point of 
boiling water, at which all living things must perish may probably be 
traced to some one or other of the mistakes above enumerated. 
Nore. One feature observed in connection with the experiments described 
was the entire absence of pellicles in the flasks at the time they were opened. 
These are always mentioned by experimenters as being associated with al] 
prolific fluids, They were searched for, but in no instance was sucha thing 
found. All the infusions remained as pellucid as on the day of their inclosure. 
The only change seen was that the fluid was, in some instances, lighter colored 
at the time of examination than when sealed, This change of color is to be at- 
tributed to the deposition of particles of matter held in suspension in the fluid: 
These deposits were, in many flasks, perceptible to the naked eye, and in some 
of them were quite large. All the fluids immediately after being filtered ap- 
peared to the naked eye free from floating particles of all kinds. But, as before 
stated, a few drops of each infusion were placed under the microscope in a 
concave cell, and an immersion lens was focussed to the bottom of the cell. 
During these examinations, but little of either organic or inorganic matter was 
at first to be seen; but if the instrument and slide were permitted to remain at 
rest and the contents of the cell examined from time to time, a gradual de- 
position of matter could be seen going on, until, at the end of an hour, the 
field of view would be found filled with organisms, and such other matter as 
was held in suspension by the fluid. 
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