SOLID TRANSPARENT MEDIA. 



53 



vent the action of surrounding atmosphere. (Fig. 26.) It is sup- 

 plied with a thermometer and with a regulator. The regulator 



FIG. 25. 



Thermostat for blood serum. 



is connected with the Bunsen burner, and keeps the thermometer 

 at a certain height. 



There are several forms of regulators in use, and new ones 

 invented continually. 



The size of the flame in some is regulated by the expansion 

 of mercury, which, as it rises, lessens the opening of the gas 

 supply. The mercury contracting on cooling allows more gas 

 to enter again. (Fig. 27.) 



Koch has invented a safety burner, by which the gas supply is 

 shut oft' should the flame accidentally have gone out. 



Coagulation of Blood Serum. The tubes of blood serum 

 having been placed in the oven, are kept at a tempera- 



