83 REVIEW. 



since 1858, been obliged to cook them in a solution of 28 per 

 cent, of salt, at a temperature of 108°, to prevent the putrefaction 

 of their contents, as in warm years nearly half of the pots pre- 

 pared were in the habit of going bad. The salt solution has been 

 found to fulfil, at the higher temperature^ all that was demanded 

 of it. In France a temperature of 117°, without salt, has been 

 found satisfactory. After reference to the work of Professor 

 Tyndall and others on this matter, Cohn goes on to show how 

 he has, since 1872, been busied, either in his own person, or that 

 of his pupils, with the study of this most interesting question ; 

 he has already proved that dense substances, such as jieas or 

 pulse, are bad conductors of heat, and that the temperature of 

 the surrounding fluid is communicated to them only with diffi- 

 culty, so that Bacteria hidden in clefts of their substance have 

 been hardly submitted to tlie temperature, which the thermo- 

 meter has marked. Dr. Horvath has dropped ijito Cohn's nutrient 

 fluid one drop of Bacteria, and has found that under such con- 

 ditions an exposure to a temperature of 6U° to 62° C. for an hour 

 lias been suflicient to destroy the power of reproduction. And 

 Dr. Schroeter, who also worked under Cohn's direction, found the 

 maximum temperature at which activity of the Bacteria was per- 

 ceptible to be 58°.^ With this we should compare the majority 

 of results, which show that 35° to 50° is the average of mortal 

 temperature, ordinary protoplasm coagulating at 43°, and other 

 protein compounds at 60° or even at 70° to 75° C. 



But we must not forget the influence of the length of time 

 during which the heat is applied, lower temperatures for longer 

 periods being within, of course, certain limits as powerful as 

 higher temperatures for shorter periods. 



3. Now comes the question. Why these contradictory results ? 

 One answer, and the fairest yet offered, is that which Cohn him- 

 self has given, namely, that the spores which are embedded in 

 firm substance, such as peas or cheese, are not acted on by the 

 heat ; and also that some forms of Bacteria, as Bacillus,^ have 

 " lasting spores," capable of resisting heat for a long time ; and 

 Dr. Boberts ('Phil. Tr.,^ clxiv, ii, p. 174) has shown the 

 extreme difficulty of ''sterilising" certain infusions of hay; to 

 these results, so scientifically conducted, Cohn has lately, with 

 the assistance of Mr. Robert Hare, a Canadian, addressed him- 

 self. For the variations in the mode of experiment which expe- 

 rience suggested I must refer the reader to the original ; suffice 

 it to say that in unboiled infusions Bacterium termo, Micrococcus, 

 Mycothri'X (rosary chain). Bacillus, and Leplothrix, were largely 

 found. Infusions that were boiled gave various results, accord- 



1 Cf. Bd. i, op. cit., Heft 2, p. 220, and Heft 3, p. 35. 



2 Cf. ' Quart. Jouru. Micr. Sci./ July, 1876, pp. 272, 273. 



