PREFACE. vi 
vestigators to do? Should they equivocate and, 
without definite trial as to the truth or untruth 
of their old belief in the destructive influence 
of boiling water, at once cast it aside? This 
would certainly seem a strange course to pursue, 
seeing that a strong belief iu the lethal effects of 
boiling water had been the measure of their 
previous profound unbelief of facts now demon- 
strated to them! Yet this course was in some 
respects the easiest—it would expose those who 
followed it to less external friction, and it allowed 
them still to hold fast to a long-cherished con- 
viction as to the truth of the dogma omne vivum 
ex vivo, which they perhaps found it impossible to 
throw aside. But whatever extenuating circum- 
stances might be pleaded, it cannot be concealed 
that the course actually adopted was not the 
method by which men of science usually pursue 
their investigations. 
The question of ‘Spontaneous Generation,’ there- 
fore, at present stands in this position. If it be 
really true that all known forms of Living Matter 
are killed by a brief exposure in the moist state 
