The four sentences (labelled $1,2,3,4$) below, when properly sequenced would yield a coherent paragraph. Decide on the proper sequencing of the order of the sentences and key in the sequence of the four numbers as your answer:
- Man has used poisons for assassination purposes ever since the dawn of civilization, against individual enemies but also occasionally against armies.
- These dangers were soon recognized, and resulted in two international declarations$-$in $1874$ in Brussels and in $1899$ in The Hague$-$that prohibited the use of poisoned weapons.
- The foundation of microbiology by Louis Pasteur and Robert Koch offered new prospects for those interested in biological weapons because it allowed agents to be chosen and designed on a rational basis.
- Though treaties were all made in good faith, they contained no means of control, and so failed to prevent interested parties from developing and using biological weapons.