THE INCUBATOR AND ACCESSORIES. 245 



Another opening serves to communicate with the interior of 

 the incubator and receives a thermometer. 



A large, well-equipped laboratory should have, in addi- 

 tion to a number of the ordinary thermostats, at least one 

 incubating room. That is to say, a room which is maintained 

 at a constant body temperature. This can be heated by 

 means of a small cylindrical stove, which is heated by a gas 

 burner and, from which hot air pipes radiate to different 

 parts of the room, A more constant temperature can be 

 maintained by passing hot- water pipes around the walls of 

 the room. The water is heated on the outside of the room 

 by means of a suitable burner. 



Thermo-regulators. — In order that a thermostat shall 

 maintain a constant temperature, it is necessary that it 

 shall be provided with a good thermoregulator. This instru- 

 ment automatically regulates the supply of , gas. The bulb 

 of the instrument, containing alcohol or mercury, is im- 

 mersed in the water between the walls of the incubator. 

 When the temperature rises, the alcohol or mercury expand 

 and shut off the supply of gas. In order to prevent the 

 gas from being cut off completely, a minute opening is 

 made in the delivery tube, thus permitting the passage of 

 a small amount of gas, which is sufficient to maintain a 

 small light. 



The simplest mercury thermo-regulator is that of 

 Eeichert. As ordinarily made, it is the exception to find a 

 Eeichert regulator that will work properly. The minimum 

 opening is invariably too large, and will, therefore, allow 

 the passage of more gas than is necessary to maintain the 

 the desired temperature. In order to obviate this difficulty, 

 a number of modifications of the Eeichert instrument have 

 been made, and some of these answer the purpose very 

 well. Unfortunately, the diameter of the delivery tube, as 

 usually made, is narrow and hence such a regulator can be 

 used only for low temperatures. 



