1885.] on Living Contagia. 163 



the air which caused flesh to putrefy. To his succeeded the far more 

 elaborate labours of Pasteur. Note the unlooked-for issues to which 

 these labours have led. With the boldness and penetration which 

 belong to genius, Lister extended to living matter the generalisation 

 established by Schwann and Pasteur in regard to dead matter. With 

 admirable clearness of vision, he pictured the atmospheric germs 

 falling upon the wounds in our hospitals and setting at nought, by 

 subsequent mortification, the skill of the best operator. ' Lister 

 insisted that the treatment after the operation was quite as important 

 as the operation itself. He devised effectual means for destroying 

 these putrefactive organisms, and thus established that antiseptic 

 system of surgery which is one of the greatest and most beneficent 

 achievements of the age in which we live. 



We now stand upon the margin of a new field which invited the 

 activity of Pasteur. In 1865, owing to a plague among the worms, 

 the silk husbandry of France had fallen into ruin. The worms 

 sickened and died wholesale ; and, because of the spots upon their skin, 

 the malady was called Pebrine. A minute corpuscular organism, 

 called Micrococcus ovatuSj had been discovered by Cornalia in the blood 

 and organs of the diseased worms, and, acquainted as he was with the 

 action of living ferments, Pasteur was prepared to see in the corpuscles 

 the cause of the plague. He followed them through all the phases of 

 the insect's life — through the egg, through the worm, through the 

 chrysalis, through the moth. He proved that the germ of the malady 

 might be present in the egg, and still escape observation. In the 

 worm also it might elude the search of the microscope. But in the 

 moth it reached a development so distinct as to render its detection 

 inevitable. From healthy moths, healthy eggs were sure to spring ; 

 from healthy eggs vigorous worms, from vigorous worms fine cocoons ; 

 so that the great problem of restoring to France its silk industry was 

 reduced by Pasteur to the separation of the healthy from the un- 

 healthy moths, the destruction of the latter and the exclusive employ- 

 ment for breeding of the eggs of the former. 



While discovering the cause of pebrine and the way to combat it, 

 Pasteur inquired how the disease was spread ; pursuing in this inquiry 

 the only way open to the investigator. He infected healthy worms 

 by smearing with corpusculous matter the mulberry leaves on which 

 they fed. He infected them by inoculation, and showed how they 

 infected each other by the wounds and scratches of their own claws. 

 Bringing together healthy and diseased worms, the healthy ones, like 

 their smitten companions, soon sickened and died. He produced 

 infection at a distance, by wafting corpusculous dust through the air. 

 All the modes by which infection is spread among human beings were 

 thus illustrated. Was it cruel to treat the healthy silkworms in this 

 fashion ? It may have been for the moment ; but Pasteur's investiga- 

 tion swept a deadly epidemic from the soil of France ; and, for the 

 units slain during the inquiry, millions have been preserved. 



In May 1876, there appeared in Cohn's ' Beitrage zur Pflanzen- 



M 2 



