CONDITIONS FAVOTJBING FEEMENTATION. 5 



In my earlier experiments, as well as in a few of those which 

 were made in connexion with this research, I had recourse to the 

 method of immersing the experimental vessels in a large beaker 

 or pan containing water and a thermometer. The temperature 

 of the water in such a vessel was raised to the required extent 

 by a spirit-lamp or gas-flame. But without frequent watching 

 and great care this method is almost sure to entail greater fluc- 

 tuations of temperature than are at all desirable. I have there- 

 fore now for some time had recourse to the ordinary incubator 

 employed in physiological laboratories, supplemented by one of 

 the ingenious and valuable gas-regulators* devised by Mr. E. J. 

 Page, B.Sc. This combination of apparatus gives us a warm 

 chamber which may be maintained almost indefi.nite]y at any given 

 temperature. The variations, extending over several weeks, may 

 with care never exceed one degree Fahrenheit. In carrying out 

 this research I have latterly found it convenient to employ two 

 incubators, in one of which the experimental fluids could be ex- 

 posed to a very high generating temperature, and in the other to 

 moderately high temperatures. 



It is more than ever necessary to employ an efficient heat- 

 regulator when the generating temperature to which the fluid is 

 to be subjected is very high, because an accidental rise even of 

 a few degrees might prove detrimental to the initiation of fer- 

 mentative changes — more especially if the fluids remained exposed 

 to this unduly elevated temperature for several hours. A caution 

 is needed, however, as regards the mode of using the incubator 

 in these experiments. A thermometer whose bulb is exposed to 

 the air of the chamber does not afibrd a correct indication of the 

 the temperature of an experimental fluid contained in a closed 

 glass vessel which has been resting for several hours upon its 

 floor. The temperature of the fluids would probably always be 

 higher than that of the air, which the thermometer registers. 

 A much more correct means of judging of the actual tempera- 

 ture of any experimental fluids contained in the incubator is 

 obtained by allowing the end of the thermometer, like the experi- 

 mental vessels, to rest upon the floor of the incubator. It is 

 of importance to regulate the temperature of the incubator in 

 accordance with the reading of a thermometer thus disposed, 

 since in the absence of such a precaution the experimen- 



* Described in Proceed, of Ohem. Soc, Jan. 1876, vol. i. p. 24. 



