THE SILKWORM ITS DISEASES AND IMPERFECTIONS. 75 



mixture over the mulberry leaves. The silkworms ate the leaves, 

 and after a time showed symptoms of the disease ; by killing and 

 microscopically examining different members of the group at 

 intervals, he was able to trace the development of the corpuscles. 



The details of one of these experiments may serve to show the 

 care with which the problem was attacked, and at last worked 

 out. On the i6th April, 1868, he infected thirty silkworms by 

 a corpusculous meal, as above. No signs of disease were manifest 

 during the first week, and even on the 25th they seemed well, 

 but the tell-tale corpuscles were detected in the intestine of two, 

 which were then examined. From this time the progress of the 

 disease became rapid, for two which were dissected on the 2yth 

 showed the corpuscles not only in the intestine, but numbers 

 of them in the silk glands as well. The next day all the rest 

 showed the black spots characteristic of pebrine. Meanwhile, 

 another set, which had been selected at the same time and from 

 the same stock, and had received an equal amount of food, but 

 had not been infected, and had been kept with scrupulous care 

 apart from the stricken set, grew rapidly and prospered, showing 

 no signs of pebrine, and being by the 3oth of April half as large 

 again as those that had contracted the disease. On the 2nd May 

 a diseased caterpillar that had just moulted for the fourth time 

 was examined. Its whole body was found to be crowded with 

 corpuscles, so that it was a marvel it had not already perished. 

 As the disease advanced the worms died, one after the other, 

 till only six of the original thirty were left. These were then 

 submitted to microscopic examination and every one was found 

 to contain corpuscles. This shows the dreadfully contagious 

 character of the disease. They had had only one corpusculous 

 meal, and yet it had been sufficient to infect them all ; not one 

 had escaped. The healthy lot, on the other hand, went through 

 all their transformations successfully, and formed fine cocoons, 

 and the moths, on being examined, were all found to be perfectly 

 healthy except two, which had no doubt become infected during 

 their larvahood by accident. 



By such experiments as these it was conclusively proved, that, 

 if the pebrine was to be eradicated, not only would it be necessary 

 to take the utmost care during the progress of any education to 

 guard the silkworms from the possibility of infection, but that only 

 such eggs ought to be reared as had been laid by females which 

 were absolutely free from taint. Pasteur's proposed method of 

 eliminating the disease, therefore, was to allow the moths to lay 

 their eggs, care being taken to identify each mother with her own 

 progeny, and then to kill the moths, crush their bodies, and 



