Accounts of the use of leeches for the medically dubious practise of blood-letting have come from China around 30 AD, India around 200 AD, ancient Rome around 50 AD and later throughout Europe. In the 19th century medical demand for leeches was so high that some areas' stocks were exhausted and other regions imposed restrictions or bans on exports, and Hirudo medicinalis is treated as an endangered species by both IUCN and CITES. More recently leeches have been used to assist in microsurgery, and their saliva has provided anti-inflammatory compounds and several important anticoagulants, one of which also prevents tumors from spreading.
When did leeches begin being used for blood-letting?
30 AD

The creation of the public sphere has been associated with two long-term historical trends: the rise of the modern nation state and the rise of capitalism. The modern nation state, in its consolidation of public power, created by counterpoint a private realm of society independent of the state, which allowed for the public sphere. Capitalism also increased society's autonomy and self-awareness, and an increasing need for the exchange of information. As the nascent public sphere expanded, it embraced a large variety of institutions; the most commonly cited were coffee houses and cafes, salons and the literary public sphere, figuratively localized in the Republic of Letters. In France, the creation of the public sphere was helped by the aristocracy's move from the King's palace at Versailles to Paris in about 1720, since their rich spending stimulated the trade in luxuries and artistic creations, especially fine paintings.
The creation of the public sphere is associated with the rise of capitalism and which other historical trend?
rise of the modern nation state

The United Nations Charter states that treaties must be registered with the UN to be invoked before it or enforced in its judiciary organ, the International Court of Justice. This was done to prevent the proliferation of secret treaties that occurred in the 19th and 20th century. Section 103 of the Charter also states that its members' obligations under it outweigh any competing obligations under other treaties.
In which centuries did a proliferation of secret treaties occur that led the United Nations Charter to include an obligation to register treaties to be invoked before it?
19th and 20th century