220 THE EVOLUTION OF LIFE 
known. I had been making experiments in re- 
gard to their death-point, though absolutely nothing 
had been said by Professor Tyndall on the subject, 
and there was no evidence to be found in his writings 
that he had even seen any of these bodies. I had 
called public attention to this fact, and his reply in 
the letter from which I have just quoted is this: 
“What he says in regard to unseen germs is also 
said without knowledge. The germs are seen 
collectively, though the microscope may fail to 
resolve them [they are most easily to be seen through 
the microscope, as Pl. I., Fig. 2 shows]. A patch of 
bluebells on a hill-slope is not the less a patch of blue- 
bells because from a distance you are only conscious 
of their colour, and fail to distinguish the individual 
flowers.” 
That was the kind of treatment of the subject 
which satisfied Professor Tyndall. On the other 
hand, the reader may now look again at pp. 78-84 fora 
record of my experiments with myriads of the actual 
Bacillus spores after they had undergone desiccation 
for over five years, as well as at pp. 75-78, giving an 
account of direct experiments on the death-point of 
these bodies when they had undergone a shorter 
period of desiccation. The results thus arrived at 
go to show that these real and veritable “ old hay 
germs ”—known to be there in their thousands—and 
after the most prolonged desiccation, were only 
found on one single occasion to have appeared to 
survive a heating to 100 C. for twenty minutes. | 
say “appeared,” because, as I have said, it is just pos- 
sible that this particular experiment may have been a 

