CH. v.] HISTORY OF SILK, ETC. 103 



quickly than was expected, as often occurs, it 

 would be advantageous then to hasten the worms 

 by heat ; for if they are allowed to delay from want 

 of heat, their first age is prolonged, and the mul- 

 berry leaf will grow and harden, and become unfit 

 for them ; the essential point is, that their progress 

 should follow that of the mulberry leaf. If cultiva- 

 tors adopt this method, they must put the eggs to 

 hatch ten days later than they would require to be 

 laid to hatch in the ordinary way, and they must 

 calculate the duration of the diff'erent ages of the 

 worm, and so manage that the completion of the 

 rearing, or fourth age, should fall into the time in 

 which the leaf has attained its full growth." 



Air. — The exhalations produced from a laboratory 

 spacious enough to contain worms proceeding from 

 an ounce of eggs, are quite astonishing. 



If one ounce of the dung taken from the wicker 

 trays be put into a bottle capable of holding one 

 pound and a half of liquid, and hermetically sealed, 

 in six or eight hours after, according to the tempera- 

 ture, the atmospherical air in the bottle will be 

 found vitiated, and totally poisonous. To deter- 

 mine this, a bird may be put into the bottle when it 

 is first opened; it will faint and die if left in it 

 many moments ; or, if a lighted candle be intro- 

 duced into it, the candle will go out directly. These 

 phenomena would not of course occur if the bottle 

 contained atmospherical air alone. 



From this it is evident that in the fifth age, the 

 laboratory before mentioned containing 1 ,200 pounds 

 of excrement, that quantity may corrupt, about 

 every eight hours, a volume of air equal to 16,800 

 Paris pints, or bottles, that are capable of holding 

 two pounds of liquid ; and in one day this quantity 

 of excrement would corrupt a volume of air equal 

 to 50,400 Paris pints. 



Having thus stated the quantity of corrupt air 

 produced by the excrement in the laboratory, it 



