STUDIES OF 1867 171 



cocoon, if it is ever so little diseased at the beginning of 

 this period, and it may be so slightly as to appear per- 

 fectly sound even under the microscope, becomes more 

 and more diseased, the few corpuscles which it contains 

 multiplying little by little within it. They invade all 

 the tissues of the chrysalis and especially those in the 

 midst of which the eggs are formed. Consequently, 

 the latter may include some of these corpuscles in their 

 interior, and the worms which are hatched from them, 

 corpuscular from their birth, cannot as we have seen, 

 reach the cocoon stage. The grower will obtain then 

 a commercial harvest from an egg only when it is pure, 

 and there is no certainty of its being pure unless it comes 

 from moths free from corpuscles. 



We are, therefore, now authorized to say that the disease 

 is contagious and hereditary, but we must give to these 

 two words, heredity and contagion, a well-defined sense, 

 for they both represent the introduction, either into a 

 sound worm from its diseased neighbors, or into an egg 

 from a corpuscular female, of one sole element, the cor- 

 puscle in process of development. Pasteur has even gone 

 farther, and by showing that at the beginning of a 

 silkworm season there are no living corpuscles except 

 those which are contained in diseased eggs he has 

 connected these two questions of contagion and heredity. 

 All other corpuscles, all, for example, which are present in 

 such great abundance in the dust of the hatcheries, are 

 dead and incapable of reproduction. It is, therefore, the 

 hereditary corpuscles alone which permit the malady 

 to assume each year its contagious character, and it will 

 disappear forever on the day when, throughout the 

 entire world, silkgrowers raise only sound eggs. 



Such are the theoretical conclusions of the experiments 

 of 1867. The practical conclusions are not less clear 

 cut. "Do you wish to know," said Pasteur to the 



