SUPRA-MAXIMAL TEMPERATURES 227 



to 130 C. the most resistant spores are soon killed. Cohn 1 observed that 

 the spores of Bacilhts subtilis, which are killed by thirty to sixty minutes' 

 boiling, may be kept for three or four days in water at 70 to 80 C. before 

 they are fatally affected. If, however, a spore germinates, its resistance 

 decreases, so that sterilization may be ensured by heating to iooC. for 

 a short time during several successive days. 



Pasteur z recognized that many bacteria were only killed by prolonged boiling, 

 which Cohn 3 and Brefeld 4 showed to be due to the high resistance of the spores. 

 Thermo-bacteria are, however, also resistant to heat in the vegetative condition. 

 The problem of disinfection has given rise to many researches in this direction 5 , 

 and these have shown that death ensues sooner in boiling water than in steam 

 at atmospheric pressure. 



The spores of various hay and potato bacteria, those of Bacillus mesentericus 

 vulgatus*, of Bacillus butylicus' 1 , and of various thermo-bacteria 8 , require from 

 a half to several hours' boiling to kill them. [It is possible that the high resistance 

 of spores is due to the relative impermeability of the spore-wall, and to the spore- 

 contents passing into a partially desiccated condition during ripening, even when 

 permanently immersed under water. That water is excreted during spore-formation 

 is evident when the entire contents of the vegetative cell contract considerably 

 to form a single spore, but this occurs also in Bacillus anthracis, whose spores 

 are only slightly resistant to boiling. If the resistance of the spore were in part 

 due to the desiccated condition of its living contents, the ultimately fatal action 

 of boiling water might be due to its causing the spore-wall to swell or become 

 permeable, the entry of water lowering the power of resistance to heat. There 

 can, however, be little doubt that the increased resistance of the spore is, in part 

 at least, due to some change in the inherent properties of its living contents apart 

 from the influence of mere desiccation. ED.] 



In very many cases the power of resistance varies at different stages 

 of development. Thus Sachs 9 and also de Vries 10 have shown that 



1 Just, Cohn's Beitr. z. Biol., 1877, Bd. n, p. 346; Cohn, ibid., p. 271. Cf. also Gruber, 

 Centralbl. f. Bact., 1888, Bd. in, p. 576. 



2 Pasteur, Ann. d. Chim. et d. Physique, 1862, 3" se"r., T. LXIV, p. 58; Etude s. 1. biere, 1876, 

 p. 34; Pasteur and Joubert, Compt. rend., 1877, T. LXXXIV, p. 206. Pasteur gives the older 

 literature, including that dealing with spontaneous generation. 



8 Cohn, 1. c., p. 250. 



4 Brefeld, Unters. ii. d. Spaltpilze, 1878, p. 10 (repr. from Sitzungsb. d. naturf. Freunde in 

 Berlin) ; Bot. Unters. ii. Schimmelpilze, 1881, Heft 4, p. 51. 



5 Cf. Fliigge, Die Mikroorganismen, 1896, 3. Aufl., Bd. I, p. 438 ; de Bary, Vergl. Morphol. u. 

 Biol. d. Pilze, 1884, p. 515. 



6 Strub, Centralbl. f. Bact, 1890, Bd. vn, p. 728. 



7 Cf. de Bary, 1. c. ; also Schattenfroh and Grassberger, Centralbl. f. Bact., 1900, 2. Abth., Bd. 

 vi, p. 411. 



8 Rabinowitsch, Zeitschr. f. Hygiene, 1895, Bd. XX, p. 154. 



9 Sachs, Flora, 1864, p. 4. 



10 de Vries, Materiaux pour 1. connaissance d. 1'influence d. 1. temperature s. 1. plantes, 1870, 

 p. 4; Sur la mort d. cellules vegetales, 1871, p. 25 (repr. from Archives Nderlandaises, T. vi). 



Q 3 



