416 Spontaneous Generation. [July, 
be rendered to the discovery of the nature of the bacteria. 
Armed with the best and most powerful appliances which the 
modern optician could supply, Dr. J. Drysdale and myself ven- 
tured on the work. The results are fully detailed elsewhere. 
It need only be remarked here that the only hope of success was 
in continuous observation of the same form, in the same drop of 
fluid under the highest powers. The secret, therefore, was to 
find a means of keeping the same drop under examination with- 
out evaporation. This we did. The result was that patient — 
work enabled us to completely unravel the life-history of six of 
these organisms. These life-cycles cannot be here recounted. 
Suffice it now to say that each of them multiplied enormously by 
self-division (fission), but that the life-cycle in each case began 
and ended in a distinct genetic product—call them what we 
choose, spores, germs, or ova. 
We have here, then, important indications of fact concerning 
the nearest allies of the bacteria: they develop from germs. 
We have, besides, the weight of the best experimental evidence 
pointing clearly to the existence of germs in the bacteria them- 
selves.. But the microscope has failed to demonstrate the latter. 
Its finest powers and finest methods failed to reach them. 
Happily at this juncture Professor Tyndall has stepped in, 
and with his accustomed brilliance and precision has opened up 
the path we need. He has presented us with a physical demon- 
stration of the existence of immeasurably minute molecules of 
matter — utterly beyond the reach of the most powerful combina- 
tion of lenses yet constructed — which are the indispensable pre- 
cursors of bacteria in sterilized infusions. In short, he has opened 
up a new and exact method, which must lead to a scientific 
determination of the existence and nature of the bacteria-germs. 
His beautiful experiments on the decomposition of vapors, and 
the formation of actinie clouds by light, led him to experiment 
on the floating matter of the air, and with what results is widely 
known. Confined and undisturbed air, however heavily charged 
with motes, becomes at length, by their deposition, absolutely 
clear, so that the path of the electric beam is invisible across 1t. 
From this, and associated indications, he acutely inferred “ that 
the power of developing life by the air, and its power of scatter- 
ing light would be found to go hand in hand;” so that a bat 
of light sent across the air into which infusions might be pla = 
g 
and examined by the eye, rendered sensitive by darkness, ™ 
1 Nature, January 27, 1876, page 252, and February 3, page 268. 
em PES 
