[ 175 ] 104 



them, slackens their work, and gives them numerous disorders, which 

 cannot easily he defined. 



3d. An atmosphere vitiated hy the fermentation of leaves and dirt, 

 or hy the later worms that lie on the litter, as well as by the defect of 

 circulation in the interior air, which renders the breathing of these in- 

 sects difficult, relaxes their organs, and also causes various diseasCvS 

 amonf'- them. In such cases, many worms drop off, others form bad 

 cocoons, die within them when they are finished, and are spoiled. 



4th. A case of very rare occurrence here, but which must be noted 

 to complete the views on this sul)jcct, is, too warm and dry an atmos- 

 phere, which dries up the worms, producing too violent a contraction 

 of the skin, not proportioned to the vacuum which increases in the 

 animal by the slow pouring out of the silky substance, and by trans- 

 piration; and thus forces them to violent and fatiguing action in the 

 formation of the cocoon; in which case they employ the reservoirs of 

 silk too fast, forcing the silk drawing tubes, producing coarser silk, 

 which thus never can have that fineness which it possesses when pro- 

 duced in a temperature of 69°. Having tried to expose a number of 

 silkworms to very dry air, at 100 degrees of temperature, several 

 thousand feet of the coai'se downy flos, or have, were obtained from 

 the cocoons by the common method of spinning; the weight of this 

 flos being six times greater than the flos obtained from cocoons form- 

 ed in a temperature of 69°. 



This observation may explain why the silk produced in very hot 

 climates is stronger and less fine than tjiat produced in temperate re- 

 gions, where the silkworms are reared at a lower degree of tempera- 

 ture.* 



The fifth age is accomplished, when the silkworm pours out its silk 

 and forms the cocoon. 



The fifth age is perfected, when, on touching the cocoon, it appears 

 to have obtained a certain consistency. The silkworm has then cast 

 its envelope, is changed into the chrysalis, and has entered its sixth 

 age. 



Qnantily of vapor and excrcmental substance emitted by Silk- 

 loorms^from the time they reach their full growth,until the form- 

 ation of the cocoon. 



The calculation resulting from facts, will here be offered, by which 

 may be ascertained the quantity of substance which issues from the 

 silkworm towards the close of the fifth age, that this calculation may 

 .show the evils which are constantly likely to attack a laboratory. 



» The above remark applies to the East India silk, the inferiority of which will be 

 noticed hereafter, in an exti-act from the Minutes of the Evidence taken before a Com- 

 mittee of the British Parliament on the Silk Trade. 



Count Dandolo has omitted a verj' important caution, which it is essential to attend 

 to when the worms begin to spin their cocoons. It is to preserve the utmost silence 

 in the apartment, as the worais are very sensible to the least noise, and, if disturbed, 

 will for a moment, cease to spin. Thus the continuity of the thread will be interrupt 

 ed, and the value of the cocoon greatly diminished. 



