14 THE CULTURE OF THE MULBERRY SILKWORM. 



The aim in culture for reproduction is to secure eggs free from 

 hereditary taint of disease, and experts only can be depended on 

 to conduct it. Besides a careful ph} T siological examination through- 

 out the rearing, the body of the mother moth is microscopically 

 tested after death, and her eggs are not retained if signs of disease 

 are discovered. In this way the birth of healthy worms is insured. 

 Pasteur first applied this method of selecting silkworm eggs, and thus 

 checked the plague (pebrine) which was rapidly destroying silkworm 

 culture in Europe. 



Formerly, through an indiscriminate use of eggs, disease invaded 

 the rearings to such a degree that from 65 to 90 pounds of cocoons 

 was considered a good yield per ounce of eggs. At the present low 

 price of silk such cultures are no longer remunerative, and industrial 

 silk culture now demands the exclusive use of scientifically tested eggs. 



The grainage, or preparation of eggs for market, constitutes a special 

 department of silk culture. In Italy there are over- -too establish- 

 ments which supply eggs to raise the annual silk crop. The poorest 

 peasant, though well skilled in the art of rearing silkworms, would 

 not risk a rearing with eggs which have not been selected and pre- 

 served by experts. 



The eggs of crossed races are best for cultures with a view to pro- 

 duction of silk, and here, as much as in the examinations which have 

 been referred to, the knowlege of experts is needed. 



The life of the egg, in those races which have but one generation each 

 3 r ear, has three phases, the first lasting about three months, full of 

 activity; the second lasting from about October to the middle of Febru- 

 aiy, one of inactivity, in which there are no signs of life; the third from 

 the middle of February to the moment of hatching, in which the vital 

 activity recommences, and the germ begins to organize as soon as the 

 temperature rises a little above 50° F. The measure of the activity 

 of the egg^ in this stage, is the measure of its danger, for any sudden 

 change of temperature would injure or destroy the delicate embryo, 

 or cause the larva to be born before its food was ready. To guard 

 against such accidents, eggs must be wintered in a high region or in a 

 refrigerator at a uniform temperature of about 35" F., from December 

 15, until the mulberry begins to bud or until hatchings are desired. 

 There should always be good ventilation, the air should not be moist, 

 and great care must be taken to keep the eggs out of the reach of mice 

 and insects. 



Natural hatchings are almost always irregular, extending over eight 

 or ten days, thus multiplying the divisions and rendering the rearing 

 difficult and costly; hence, the necessit}^ for artificial incubation. 



Eighteen days before the time decided on for the hatching, spread 

 out the eggs in thin layers in the incubating room or incubator. The 

 temperature should be 55° F. 



