80 BIOLOGY AND TECHNIQUE 



temperature for temperature. For the recognition of this fact we 

 are largely indebted to the early researches of Koch and Wolif- 

 hiigel, 22 and of Koch, Gaffky, and Loeffler. 23 



These observers were able to show that the spores of anthrax 

 were destroyed by boiling water at 100 C. in from one to twelve 

 minutes, whereas dry hot air was efficient only after three hours' 

 exposure to 140 C. Extensive confirmation of these differences has 

 been brought by many workers. An explanation of the phenomena ob- 

 served is probably to be found in the changes in the coagulability 

 of proteins brought about in them by the abstraction of water. 

 Lewith, 24 working with various proteins, found that these substances 

 are coagulated by heat at lower temperatures when they contain 

 abundant quantities of water, than when water has been abstracted 

 from them. On the basis of actual experiment with egg albumin 

 he obtained the following results, 25 which illustrate the point in 

 question : , 



Egg albumin in dilute aqueous solution, coagulated at 56 

 " " with 25 per cent water, " 74 



tt (t 18 < ( n tt 8 o 



C. 



74-80 C. 

 tt 8 o_ 90 o C- 



Absolutely anhydrous albumin, according to Haas, 26 may be 

 heated to 170 C. without coagulation. It is thus clear that bacteria 

 exposed to hot air may be considerably dehydrated before the tem- 

 perature rises sufficiently to cause death by coagulation, complete 

 dehydration necessitating their destruction possibly by actual 

 burning. 



Bacteria exposed to moist air or steam, on the other hand, may 

 absorb water and become proportionately more coagulable. 



The same principle, as Lewith points out, probably explains the 

 great resistance to heat observed in the case of the highly con- 

 centrated protoplasm of spores. 



Apart from the actually greater efficiency of moist heat when 

 compared with dry heat of an equal temperature, an advantage of 

 great practical significance possessed by moist heat lies in its greater 



22 Koch and Wolff Mgel, Mitt. a. kais. Gesundheitsamt, I, 1882. 



23 Koch, Gaffky and Loeffler, ibid. 



24 Lewith, Arch. f. exp. Path. u. Pharm., xxvi, 1890. 



25 Lewith, loc. cit., p. 351. 



26 Haas, Prag. med. Woch., 34-36, 1876. 



