§ 110. Apart from such means as are expressly prohibited by treaties or custom, all means of killing and wounding that exist or may be invented are lawful. And it matters not whether the means used are directed against single individuals, as swords and rifles, or against large bodies of individuals, as, for instance, shrapnel, Gatlings, and mines. On the other hand, all means are unlawful that render death inevitable or that needlessly aggravate the sufferings of wounded combatants. A customary rule of International Law, now expressly enacted by article 23 (_e_) of the Hague Regulations, prohibits, therefore, the employment of poison and of such arms, projectiles, and material as cause unnecessary injury. Accordingly: wells, pumps, rivers, and the like from which the enemy draws drinking water must not be poisoned; poisoned weapons must not be made use of; rifles must not be loaded with bits of glass, irregularly shaped iron, nails, and the like; cannons must not be loaded with chain shot, crossbar shot, red-hot balls, and the like. Another customary rule, now likewise enacted by article 23 (_b_) of the Hague Regulations, prohibits any treacherous way of killing and wounding combatants. Accordingly: no assassin must be hired and no assassination of combatants be committed; a price may not be put on the head of an enemy individual; proscription and outlawing are prohibited; no treacherous request for quarter must be made; no treacherous simulation of sickness or wounds is permitted. [Sidenote: Explosive Bullets.] § 111. In 1868 a conference met at St. Petersburg for the examination of a proposition made by Russia with regard to the use of explosive projectiles in war. The representatives of seventeen Powers--namely, Great Britain, Russia, Austria-Hungary, Bavaria, Belgium, Denmark, France, Greece, Holland, Italy, Persia, Portugal, Prussia and the North German Confederation, Sweden-Norway, Switzerland, Turkey and Württemberg (Brazil acceded later) signed on December 11, 1868, the so-called Declaration of St. Petersburg,[239] which stipulates that the signatory Powers, and those who should accede later, renounce in case of war between themselves the employment, by their military and naval troops, of any projectile of a weight below 400 grammes (14 ounces) which is either explosive or charged with fulminating or inflammable substances. This engagement is obligatory only upon the contracting Powers, and it ceases to be obligatory in case a non-contracting Power takes part in a war between any of the contracting Powers. [Footnote 239: See above, vol. I. § 562, and Martens, _N.R.G._ XVIII. p. 474.] [Sidenote: Expanding (Dum-Dum) Bullets.]