

SOLID TRANSPARENT MEDIA. 



51 



vent the action of surrounding atmosphere. (Fig. 22. ) It is sup- 

 plied with a thermometer arid with a regulator. The regulator 



FIG. 21. 



Incubator 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 is regulated by the expansion ot mer- 

 cury, which, as it rises, lessens the opening of the gas supply. 

 The mercury contracting on cooling allows more gas to enter 

 again. (Fig. 23.) 



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

 shut off should the flame accidentally have gone out. 



Coagulation of Blood Serum, The tubes of blood serum 

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



