certain Fibrous Substances when wetted. 375 



substances have for water when dry causes heat to be generated 

 when they are surrounded by saturated steam ; and thus causes 

 the steam which penetrates into their interstices to be converted 

 from saturated into superheated steam. 



The source of the heat generated when fibrous organic 

 materials are wetted by coming in contact with water vapour is 

 not only the latent heat of vapour converted into the liquid state, 

 for a generation of heat occurs when very dry filter paper, flannel 

 or cotton is wetted with water. Thus a little roll of filter paper 

 was thoroughly dried in hot air and cooled over sulphuric acid. 

 A thermometer was inserted so that the bulb was in the centre of 

 the roll. The roll was then taken out, and flooded with water at 

 a temperature slightly lower than that of the roll. Nevertheless 

 the thermometer rose almost immediately 5° C. Similar results 

 have been obtained with other organic materials, but not with 

 asbestos. It seems probable from this experiment that the 

 source of the heat in question is to be found partly in the latent 

 heat of water converted into the solid state. On the ground of 

 Dr Dudgeon's experiment a similar conclusion was reached by 

 Sir W. Roberts, who wrote (loc. cit.), " it is probable that with the 

 superexsiccated flannel the first portions of the aqueous vapour 

 condensed at the beginning of the experiment pass from the 

 gaseous into the solid form and constitute that portion of water 

 which is incorporated in intimate union with all organic tissues." 



How far the results related in this paper are due to the salts 

 present in the materials used has not been ascertained. 



These observations have some bearing on practical disinfec- 

 tion. Superheated steam, as was shown by Von Esmarch 1 , has 

 a very inferior sterilising action to that of saturated steam, but 

 some experiments which I have made in conjunction with Dr 

 J. H. C. Dalton 2 have shown that this only applies to the outside of 

 such articles as pillows, rolls of blanket, etc., for in the interior 

 the temperature does not exceed 100° C, no matter how much 

 higher that of the outside may be ; the microbes are therefore 

 exposed there to saturated and not to superheated steam ; and in 

 our experiments dried Anthrax Spores in the interior of the 

 pillows etc. were always quickly killed, while those on the surface 

 sometimes escaped. 



Again, under the opposite conditions, namely when very dry 

 organic material is put into saturated steam, the experiments 

 have shown that Anthrax Spores within a little roll of flannel 

 bandage may escape death, when the roll has been placed in 

 saturated steam for 10 minutes and a thermometer in the im- 



1 Zeitschf. /. Hygiene, 1888, pp. 196 and 399. 



2 Lancet, Feb. 3, 1900. 



