78 



GENERAL MANAGEMENT OF POULTRY. 



every twelve hours, and not oftener ; and if many are to be 

 taken out, the "vital heat" thus abstracted must be com- 

 pensated by more hot water than would otherwise be used. 

 All these points are simple enough, and easily remembered 

 when their reason is once clearly seen ; but in their observance 

 lies the main secret of success with hot-water incubators. 



Simple as this system was, however, the provision of 

 gallons of boiling water every twelve hours was found such a 



Fig. 16. Toralinson's Incubator. 



tax on most householders, that there was a demand on all 

 hands for supplementary apparatus. The first and most 

 natural step was to supply special boilers heated by paraffin 

 oil, or Fletcher's well-known gas-furnaces ; and these are still 

 considerably used. The further step was, however, soon taken 

 of carrying circulating pipes from a small boiler into the tank 

 of the machine, and this is now the favourite and usual method 

 of working hydro-incubators. Instead of withdrawing from 

 three to six gallons of water, to be replaced by boiling every 

 twelve hours, at the same periods the lamp under the boiler is 

 lit for a short time, so as to convey more heat into the tank, 



