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Chapter XVII. 

 THE DEVELOPMENT OF THE CHICK. 



I. PRACTICAL INSTRUCTIONS. 



The following apparatus is requisite and should be adjusted 

 before the eggs are inserted. 



An incubator {those made by Hear son are the best), the 

 temperature of which must be maintained constant at 41 "5 C. 

 (or 103-105 F,) by a reliable thermostat. Each egg should have 

 the date of insertion written in pencil. A number of metal 

 stands with small gas jet under each and connection for gas 

 tubing, though not essential, are desirable to carry the dishes 

 of warm salt solution, in which the eggs are to be placed during 

 examination. A convenient size is 8| inches by 6 inches, with 

 a flange of 1 inch width to support it, and covered on three sides 

 in order to screen the flame below from draughts. 



A corresponding number of enamelled dishes, each with a 

 plaster of Paris mould to carry the egg. These moulds are 

 easily made by pouring the plaster into a small dish and depress- 

 ing the surface with a pot egg. A thermometer may be placed 

 in each dish, and warm 75 per cent, salt-solution added. The 

 dish is placed on the warm stage, the gas jet lit and turned down, 

 and the dish allowed to rise to the desired temperature. When 

 this is reached the gas must be reduced to a very minute flame. 



Instruments, watch-glasses, and slides are also required, 

 together with some gummed paper. The most useful fixative 

 is perhaps picro-sulphuric (100 vols, of concentrated picric 

 acid and 2 vols, of strong sulphuric acid ; the precipitate is 

 filtered off and the filtrate diluted with thrice its volume of 



