78 THE EVOLUTION OF LIFE 
clear, and showed no signs of turbidity during the 
ten days that they were retained in the incubator. 
Thus thousands of Bacilli spores, after they had 
undergone a very considerable amount of desiccation, 
were found to be unable to survive a heating to 
212 F., prolonged for only twenty minutes. 
(c) Death Pownt of Spores of Bach after Desiccation 
Jor a prolonged period 
About the same time that these experiments 
were made (towards the middle of 1877) Professor 
Tyndall had much to say concerning “old hay 
germs,” as a consequence of his having made ex- 
periments with some five-year-old hay, which yielded 
results he could only explain by imagining that 
certain Bacillus germs, not seen and examined by 
him, but supposed to be contained in the hay, had, 
by reason of their prolonged desiccation, been able 
to withstand the temperature of boiling water even 
for seven or eight hours, and thus to have been the 
cause of the appearance of swarms of Bacilli within 
his experimental vessels. 
Recognising, at this time, the futility of further 
discussion on such a point till exact experiments 
bearing upon the question had been made of a kind 
similar to those just recorded—except for the fact 
that the Bacillus spores had actually undergone 
desiccation for a number of years rather than days— 
I caused another hay infusion to swarm with such 
bodies, and subsequently poured some of this fluid 
out upon six microscope slips, so as to form a thin 
stratum on each. After the fluid had evaporated, 

