52 Lectures on Bacteria. [$ vi. 



extreme high temperatures. Most of them continue capable of 

 germination after being heated in a fluid up to iooC. ; some 

 will bear 105 C., uoC., and as much as i3oC. 



These are all general rules and are not affected by the modi- 

 fications and exceptions which occur in different cases, and 

 which in part depend on the species and individual, other con- 

 ditions remaining the same, in part also are found in the same 

 species, being then dependent on the external conditions, such 

 especially as the length of the time during which they are heated, 

 dried, or soaked, and in the latter case on the nature of the 

 surrounding fluid. 



There are first of all species which develope vigorously at a 

 temperature considerably above 50 C. Cohn and Miquel supply 

 instances of this, but the best is that of a Bacillus described by 

 van Tieghem (23), which grows and forms spores in a neutral nu- 

 trient solution at a temperature of 74C.; growth ceases at 77C. 



The Bacilli obtained by Duclaux (24, 25) from cheese, and 

 named by him Tyrothrix, are instructive examples on all the 

 points above-mentioned. The vegetative cells of T. tenuis 

 cultivated in a neutral fluid were only killed at a temperature of 

 90-95 C., in a slightly alkaline fluid they bear a temperature 

 of over iooC., while the ripe spores remain capable of germin- 

 ation when subjected to a temperature of 115 C. in a similar 

 fluid. The most favourable temperature for vegetation in this 

 species is 25-35 C. T. filiformis in the vegetative state will 

 bear a temperature of iooC. in milk, but is killed in the space 

 of a minute in an acid fluid at the same temperature. The 

 spores of this species are uninjured at a temperature of i2oC. 

 in milk, but are killed at less than 110 C. in gelatine. Duclaux 

 gives similar accounts of other species. The vegetative cells also 

 of Bacillus Anthracis are said by Buchner (28, p. 229) to continue 

 capable of infection when heated for an hour and a half in 

 neutral and slightly acid fluids up to a temperature of 75-80 C. 

 Brefeld (19) found all the spores of Bacillus subtilis in a nutrient 

 solution kept for a quarter of an hour at a temperature of 



