INCUBATORS HEATED BY ELECTRICITY 65 



from joints and other causes, it is apparent that the apparatus requires careful 

 supervision. 



3. In time the elasticity of the lamina diminishes, with the result that the 

 temperature is not controlled. 



D. Roux's incubator. Roux's incubator meets all practical requirements, 

 and has none of the disadvantages of Babes' and d'Arsonval's, and for these 

 reasons is preferable to those instruments. 



The incubator consists of a rectangular wooden box, closed in front by a 

 single or double glass door raised on feet and heated below by a gas burner. 

 The inside walls are lined by a series of vertical copper tubes. The air in the 

 incubator is maintained at a constant temperature by radiation from these 

 tubes, which are heated by the gases from the burners below passing up 

 through them. Ventilation is provided through holes in the floor and roof. 



For details of the regulator, see p. 60. 



Method of use. 1. Before using the incubator, it is well to paste black paper over 

 the doors to shield the cultures from light, which may have an adverse influence on 

 their growth. 



2. Lay a thermometer on each shelf to watch the rise of temperature. When 

 the incubator is finally regulated, each shelf has an absolutely constant tem- 

 perature, which differs slightly from that of the shelf above and below. 



3. The tube C (fig. 48, p. 61) is connected to a gas tap, and the tube D to the 

 burners beneath the incubator. Adjust the screw S controlling the piston E, and 

 turn it until the latter is widely open. 



4. Light the gas. 



5. When the temperature on the middle shelf registers half-a-degree below the 

 temperature required (36'5 C. if a temperature of 37 C. is required), turn the 

 screw S until the piston E is closed, and the burner is fed only by the by- pass V. 

 But when the temperature in the incubator falls, the limbs of the metal U separate, 

 the rod T presses on the piston rod, with the result that the piston E is opened, and 

 a larger volume of gas reaches the burner. The apparatus is now regulated, and 

 the temperature will remain constant without further supervision. If the gas be 

 turned off at the main and then relit, the temperature will be regulated at the 

 height at which it stood when the gas was turned off. A little vaseline must be 

 applied to the piston chamber from time to time to lubricate the piston rod. 



SECTION III. INCUBATORS HEATED BY ELECTRICITY. 



When a laboratory has electric power laid on, it may be convenient to use 

 incubators such as those of d'Arsonval, Regaud, Fouilliaud [or Hearson] 

 which can be heated with electricity. 



A. D'Arsonval's electrical incubator is similar in appearance to Roux's 

 incubator. It is fitted below with a drawer in which the special form of lamp 

 used for heating the incubator is placed. A metallic regulator is interposed 

 in the circuit : as the temperature rises it causes the expansion of a metal 

 rod, and this breaks the circuit and cuts off the current. When on the 

 other hand the temperature falls the bar returns to its normal position in 

 contact with a platinum point, and the circuit is re-established. To regulate 



'the incubator a screw is turned until the current passes. When a thermometer 

 placed in the incubator registers a few degrees below the temperature required, 

 the screw is slightly reversed. The temperature is noted again in about 

 half-an-hour's time, and after a few trials the regulation is quite perfect. 



B. Hearspn's electrical incubators. Hearson's regulator (p. 62) can be 



applied to incubators heated by electricity. The circuit is broken and the 

 current cut off when the lever is raised by the expansion of the fluid in the 

 capsule. 



