70 THE EVOLUTION OF LIFE 
much by the known method of fission as by any 
unknown and assumed method of reproduction. 
As I then said: ‘“‘ These experiments seem to show, 
therefore, that even if Bacteria do multiply by means 
of invisible gemmules as well as by the known 
process of fission, such invisible particles possess 
no higher power of resisting the destructive influ- 
ence of heat than the parent Bacteria themselves 
possess.” } ; 
Nothing more than this could be said in 1871; 
though five years later memoirs were published by 
Professor Cohn? and Dr Koch making known the 
existence of easily visible ‘‘ spores,” both in hay and 
in anthrax Bacillii When these organisms are 
cultivated at blood-heat, and the infusions are 
exposed to air filtered through a cotton-wool plug, 
both these forms of Bacilli tend to grow into long 
interlacing threads at the surface of the fluid; and 
in twenty-four to forty-eight hours a number of 
highly refractive particles appear at short distances 
from one another within the threads—which are the 
“spores” in question. Subsequently, similar bodies 
have been found in many other Bacilli and, among 
them, in the thermophilic Bacilli to which reference 
has recently been made. 
It remains, therefore, to ascertain what amount 
of heat these spores are capable of withstanding, 
first of all (a2) when in their moist state, and 
subsequently (6) after they have undergone desic- 
cation. 
1 “ Modes of Origin of Lowest Organisms,” 1871, p. 60. 
2 “ Beitr. sur Biologie der Pflanzen,” 2* Bd., p. 268. 

