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its dust, and not in . its gaseous ingredients ; but as to the 
exact nature of that biogenic power — whether it be a speci- 
fic germ or a ferment— no sufficient evidence has yet been 
adduced. Dr. Roberts did not find that diminished pressure 
of the atmosphere, obtained by sealing flasks hermetically 
in ebullition, after the mode suggested by Dr. Bastian, 
materially affected the results. 
Dr. R, Angus Smith, F.R.S., said that he was glad to see 
such uniformity of results. His own experiments, which 
were very numerous on a similar point, were made differ- 
ently, but were without exception proving the same. As 
to the name of the substances in the air, he preferred germ : 
it involved no theory. A germ may be considered that 
which germinates. Dust is an equivocal expression, which 
may cause a popular error. Polarity introduces a theory 
which is so entirely without basis that in our present state 
of knowledge we may call the inference it presupposes 
decidedly false. 
“P.S. To Dr. Joule’s description of a Mercurial Air- 
pump.” 
The exhauster described in the last number of the Pro- 
ceedings has been further improved by dispensing with the 
glass tube e, and its stop-cock /. This is effected by attach- 
ing the base of the globe b to a strengthened indiarubber 
pipe, connected at the other end to a glass vessel of rather 
larger capacity than b. This vessel has only to be succes- 
sively raised and lowered in order to exhaust the receiver. 
The mercury in the vessel may be either under atmospheric 
