258 Tue Microscope. 
known. We did not know biologically how they developed: 
And yet with this great deficiency it was considered by some 
that their mode of origin could be determined by heat experi- 
ments on the adult forms. Roughly the method was this. It 
was assumed that nothing vital could resist the boiling point of 
water. Fluids containing full grown organisms in enormous 
multitudes, chiefly bacteria, were placed in flasks, and boiled 
for from 5 to 10 minutes. While they were boiling the necks 
of the flasks were hermetically closed, and the flask was allowed 
to remain unopened for various periods. The reasoning was: 
Boiling has killed all forms of vitality in the flask. By the her- 
metically sealing nothing living can gain subsequent access to 
the fluid; therefore, if living organisms do appear when the 
flask is opened, they must have arisen in the dead matter de 
novo by spontaneous generation. But if they do never so arise 
the probability is that they originate in spores or eggs. Now it 
must be observed concerning this method of inquiry that it 
could never be final; it is incompetent by deficiency. Its re- 
sults could never be exhaustive until the life-histories of the 
organisms involved were known. And further, although it is a 
legitimate method of research for partial results, and was of ne- 
cessity employed, yet it requires precise and accurate manipu- 
lation. A thousand possible errors surround it. It can only 
yield satisfactory results in the hands of a master in physical 
experiment. And we find that when it has secured the requi- 
site skill, as in the hands of Prof. Tyndall for example, the re- 
sult has been the irresistible deduction that living things have 
never been seen to originate in not-living matter. Then the 
ground is clearer for the strictly biological inquiry, How do 
they originate ? 
To answer that question we must study the life-histories of 
the minutest forms with the same scrutiny and thoroughness 
with which we study the development of a crayfish or butter- 
fly. The difficulty in the way of this is the extreme minute- 
ness of the organisms. We require powerful and perfect lenses 
for the work. Happily during the last fifteen years the im- 
provement in the construction of the most powerful lenses has 
been great indeed. Prior to this time there were English lenses 
that amplified enormously. But an enlargement of the image 
