These experiments, I repeat, threw a strong light on the nature of the disease, and exactly accounted for what took place in the industrial cultivations. From the malady which attacked the worms at their birth, decimating a whole cultivation, down to the invisible disease that may be said to inclose itself in the cocoon, all was now explained. One of the effects of the plague which had most excited the surprise and thwarted the efforts of cultivators was the impossibility of finding productive eggs, even when they tried to obtain them from the cocoons of groups which had succeeded perfectly well as far as the production of cocoons was concerned. It was proved that almost invariably the following year the eggs of these fine-looking groups were unproductive. Numbers of the agricultural boards, and practitioners, not being able to believe in the existence of the disease in collections that were so satisfactory as regards the abundance and beauty of the cocoons, persisted in thinking that the failures had an origin not connected with the seed itself. This resulted in deception after deception, often even in mistakes that were much to be regretted. Frequently the best husbandmen were known to reserve for the production of eggs some very fine cultivations, not having observed in the worms either spots of _pébrine_ or corpuscles even up to the time when the mounting of the brambles had been accomplished; and the year following they had the pain of seeing all the cultivations from these eggs perish. These circumstances, so well calculated to produce discouragement and to give the disease a mysterious character, met with their natural explanation in the facts proved by experimental infection. Still, as it never occurs to the cultivator to infect the worms directly by giving them food charged with corpusculous débris, it might be asked how, in the industrial establishments, such results can be produced. Pasteur lost no time in solving this difficulty. In a cultivation containing corpusculous worms these worms perpetually furnish contagious matter, which falls upon the leaf and fouls it. This is the excreta of the worms, which the microscope shows to be more or less filled with corpuscles drawn from the lining of the intestinal canal. It is there that they swarm. It is easy to understand that these excreta, falling on the leaves, contaminate them all the more easily because the worms, by the weight of their bodies in crawling, press the excreta against the leaves. This is one cause of natural contagion. By the excreta of corpusculous worms which he crushed, mixed with water, and spread with a paint-brush over the mulberry leaves intended for a single meal, Pasteur was able to communicate the contagion to as many worms as he liked.