On the French Alps a sweet exudation is found on the small branchlets of young larches in June and July, resembling manna in taste and laxative properties, and known as Manna de Briancon or Manna Brigantina; it occurs in small whitish irregular granular masses, which are removed in the morning before they are too much dried by the sun; this manna seems to differ little in composition from the sap of the tree, which also contains mannite; its cathartic powers are weaker than those of the manna of the manna ash (Fraximus ornus), but it is employed in France for the same purposes.
A large portion of the plain, being an alluvial deposit, is extremely fertile, but in the neighbourhood of the sea the saline exudation common in the north of China renders futile all attempts at cultivation.
The seeds when placed in water for some time become coated with glutinous matter from the exudation of the mucilage in the external layer of the epidermis; and by boiling in sixteen parts of water they exude sufficient mucilage to form with the water a thick pasty decoction.
The tree is a native of the islands and shores of the Mediterranean, passing eastward into Central Asia; but the resinous exudation found in commerce is collected in the island of Chios.
When, towards the end of his student-days in Berlin, he was acting as clinical assistant in the eye department of the Berlin Hospital, he noticed that in keratitis and corneal wounds healing took place without the appearance of plastic exudation.