18 UTILIZATION OP MINUTE LIFE. 



attention to this question, has lately submitted to 

 analysis the air of the rooms in some of the prin- 

 cipal silkworm establishments in France, and has 

 found that in many cases this air was devoid of the 

 necessary proportion of oxygen. Indeed, these 

 establishments will never be properly warmed and 

 ventilated unless they adopt the Van Hecke system 

 of ventilation and warming, which is beginning to 

 be generally employed in hospitals, and which is the 

 only system of mechanical ventilation where the 

 heat and the supply of air are completely under 

 control, and can be regulated at will.* 



The period which elapses from the birth of the 

 larvee to the time it begins to spin, varies according 

 to the different climates, and according to the par- 

 ticular species or variety of silkworm cultivated. 

 In China this period is reckoned at twenty-four 

 days j in Italy from thirty to thirty-two days ; and 

 in the North of France and Belgium from thirty- 

 two to thirty-four days. In Belgium the culture of 

 the silkworm has begun upon a large scale ; there 

 is an extensive establishment in Uccle near Brussels 

 (see Fig. 1), which is the most northern establish- 

 ment of the kind in Europe. 



During this period the grubs change their skin 

 four times, and their appetite, which is enormous, 

 becomes still greater after each moulting. For- 

 * See " Medical Eeview," January, 1861, London. 



