176 THE EVOLUTION OF LIFE 
addressed by me to the Academy (see p. 154). But 
in regard to his own experiment he says, “En 
operant comme je vais le dire, l’expérience réussit 
cent fois sur cent, mille fois sur mille, c’est a dire que 
jamais elle ne donne des bactéries.” This boastful 
statement I can readily believe, simply because it is 
easy invariably to obtain negative results when a 
wrong method is employed, though it is not always 
possible to obtain invariably uniform results, even 
with a right method, when dealing with a fluid 
naturally subject to more or less variation. 
According to his own statements, M. Pasteur fell 
into the same error as that which caused Sir William 
Roberts and Professor Tyndall invariably to find 
their fluids barren: he also added potash in excess. 
It is easy to make this plain. 
He began by providing a solution of potash suff- 
cient to neutralise 15 cubic centimetres of urine which 
had been boiled for ten minutes in an open vessel, 
instead of an amount distinctly short of full neutralisa- 
tion, as | had advised; but he did not add the potash 
till he had boiled the urine again for another 10 
minutes, and this time in a vessel closed with a plug 
of cotton-wool, which, as I have shown (p. 112), would 
raise the boiling-point at least 2° or 3° C.,and thus cause 
a very distinct lowering of the acidity of the urine. 
The extent of the lowering of acidity thus produced 
may be judged from the extent of lowering shown on 
p. 171 to have been produced by boiling an ounce of 
urine in a retort with a capillary neck for 5 minutes 
only. The inevitable result of Pasteur’s method 
would have been so to diminish the acidity of the 
