He also indicated another natural and direct cause of contagion. The six fore-feet of the worm have sharp hooks at their ends, by means of which the worms prick each other's skins. Let any one imagine a healthy worm passing over the body of the corpusculous worm. The hooks of the first worm, by penetrating the skin of the second, are liable to be soiled by the corpuscles immediately below that skin; and these hooks are capable of carrying the seeds of disease to other healthy worms, which may be pricked in their turn. To demonstrate experimentally, as Pasteur did, the existence of this cause of contagion, it was only necessary to take some worms and allow them to wound each other. Lastly, infection at a distance, through the medium of the air and the dust it carries, is a fact equally well established. It is sufficient, by sweeping the breeding-houses, or by shaking the hurdles, to stir up the dust of corpusculous excretions and the dried remains of dead worms, and to allow them to be spread over the hurdles of the healthy worms, to cause, after a certain time, contagion to appear among these worms. When very healthy worms were placed in a breeding nursery at a considerable distance from unhealthy worms, they, in their turn, became infected. After so many decisive experiments it was no longer possible not to see in _pébrine_ an essentially contagious disease. Nevertheless, among facts invoked in favour of non-contagion, there was one which it was difficult to explain. There existed several examples of successful cultivations conducted in nurseries which had totally failed from the effects of _pébrine_ the year before. The explanation is, as shown by Pasteur, that the dust can only act as a contagion when it is fresh. Corpusculous matter, when thoroughly dried, loses its virulence. A few weeks suffice to render such matter inoffensive: hence the dust of one year is not injurious to the cultivations of the next year. The corpuscles contained in the eggs intended for future cultivation alone cause the transmission of the disease to future generations.