56 THE EVOLUTION OF LIFE 
perimented (belonging to the genera Urtica, Trades- | 
cantia, "and Vallisneria) was similarly killed and 
altered by a very brief exposure to a temperature of 
1184 F. as a maximum. 
We now have to approach the problem to which 
the other investigations already cited are to be re- 
garded as necessary and illuminating preliminaries, 
We have to ascertain, that is, (a) the limits of resist- 
ance to heat, when in the moist state, of Bacteria 
and Torule; and (4) the more difficult problem of 
the resistance to heat under similar conditions of 
germs of Bacteria and Fungi, both before and after 
they have been submitted to desiccation— Bacteria 
or Moulds (such as are shown in Plate I.) being the 
organisms that are prone to appear within our 
experimental vessels, and the secret of whose origin 
we are striving to discover. 
Lhe Thermal Death-point of Bacteria and 
Fungus-germs int the Moist State 
It has now been very definitely ascertained that 
certain fluids exist which, after they have been 
boiled, never even seem to give birth to Bacteria, 
although they continue to be quite suitable for the sup- 
port and active multiplication of any such organisms 
that may subsequently have been added to them. 
Among such fluids I may name one commonly known 
as ‘‘ Pasteur’s solution,” and also a much simpler one, 
which I have myself more commonly used, consisting 
merely of ten grains of neutral ammonium tartrate and 

