A Chinese book published on the rearing of silkworms contains a series of little practical counsels. 'The person who takes care of the silkworms,' says this guide to the perfect cultivator, 'ought to wear a simple garment, not lined. He must regulate the temperature of the spinning-house according to the sensation of heat or cold which he experiences; if he feels cold, he may conclude that the worms are cold, and he will increase the fire; if he feels hot, he will conclude that the worms are hot, and he will suitably diminish the fire.' One point which had been ignored before the experiments of Pasteur was the contagious character of _flacherie_. This contagion may surpass that of _pébrine_ itself as regards duration. In _pébrine_ the dried corpusculous matter loses all virulence after the lapse of some weeks. The disease cannot, therefore, communicate itself from one year to another by the corpusculous dust of a rearing establishment. The germs, on the contrary, of the microscopic organisms which provoke fermentation in the mulberry leaves, especially the vibrios, retain their vitality for several years. The dust of a silkworm nursery infected by _flacherie_ appears under a microscope quite full of cysts or spores of vibrios. These spores or cysts rest, like the sleeping beauty in the forest, until a drop of water falls upon them and awakens them into life. Deposited on the leaves which are to serve as nourishment, these germs of vibrios are carried into the intestinal canal of the worm, develop and multiply themselves, and completely disturb the digestive functions, unless the digestion is so strong that the germs are immediately arrested, and disposed of like the food itself. This is what happens when the worms are in full vigour. It is a struggle for life, in which the worms often gain the victory. Giving to some very healthy worms a meal of leaves covered with the dry dust of a silkworm nursery, infected the year before by _pébrine_ and _flacherie_, Pasteur reproduced _flacherie_, and not _pébrine_. Still more readily did he produce the first of these maladies, when he gave, as food, leaves polluted by the contents of the intestinal canal of worms which had died of the disease. As in the case of _pébrine_, the excreta of the worms attacked by _flacherie_, defiling the leaves, carry the mischief to the healthy worms, or add to the dangerous fermentation in the intestines of those which are already in part attacked.