74 SILKWORMS. 



cocoons, a return which, for that year alone, represents a loss of 

 at least a hundred millions of francs. The question, therefore, 

 was really one of national importance ; remedy after remedy had 

 been tried in vain ; there was no end to the nostrums that were, 

 one after the other, confidently announced as the infallible cure, 

 only to be found on trial absolutely valueless. " Gases, liquids, 

 and solids," writes a French authority in 1860, "have been laid 

 under contribution. From chlorine to sulphurous acid, from 

 nitric acid to rum, from sugar to sulphate of quinine all has been 

 invoked in behalf of this unhappy insect." But all this was pro- 

 ceeding in the dark ; what was needed was a thoroughly scientific 

 investigation of the whole question, to determine the obscure 

 cause and mode of origin of the disease, and then there might be 

 some hope of successfully battling with it. It is no wonder, 

 therefore, that Dumas, who saw in Pasteur just the man for such 

 an investigation, urged it upon him with all the energy in his 

 power, until, notwithstanding Pasteur's attempt to excuse himself 

 on the ground that he knew nothing at all about silkworms, he at 

 length prevailed upon him to undertake the task. 



It had already been made out that the corpuscles might appear 

 even in the egg, and it had been supposed that if eggs did not 

 reveal any corpuscles when microscopically examined, they were 

 therefore free from infection and their incubation might be under- 

 taken with every hope of a successful result. But this test, for 

 some reason not understood at the time, often deceived those who 

 put trust in it, and was never widely .adopted. Pasteur, however, 

 soon proved that it was quite possible for the egg, and even the 

 worm itself, to be diseased, without the corpuscles being rendered 

 visible by the microscope, and that therefore it was not at all safe 

 to argue the healthiness of a batch of eggs from the absence of 

 visible corpuscles. But he noticed also that the corpuscles 

 increased in size with the growth of their host, being larger in the 

 chrysalis than in the caterpillar, and largest of all in the moth. 

 He therefore determined to deal with the moths rather than with 

 the eggs, in his endeavour to stamp out the disease. 



With the utmost care and precision he followed the different 

 steps in the development of the corpuscles. He obtained a large 

 series of perfectly healthy caterpillars from eggs of moths which, 

 by microscopical examination, had been proved to be free from 

 taint. From these he selected sets of twenty or thirty to experi- 

 ment with. He introduced the disease into the trial set by giving 

 them a meal impregnated with the corpuscles. Taking a small 

 caterpillar already suffering from the disease, he crushed it and 

 pounded up its body with water, and then smeared a little of the 



