In all modern armies infantry is, in virtue of its numbers and importance, the principal arm. Since the introduction of firearms, infantry has gradually increased in importance and numbers as compared with the other arms. In the Thirty Years’ war, the proportion of cavalry to infantry was as 1:1, or 1:2, and frequently the cavalry even predominated. In the Swedish army one gun per 1,000 men was considered sufficient. During the era of linear tactics in the 18th Century the proportion between the two principal arms had become as 1:2 and 1:3; in the Napoleonic wars as 1:6 and 1:8. The number of guns was increased to 4 per 1,000 men. In the course of a campaign the ratio changes to the disadvantage of infantry. At the outbreak of the war of 1870-71, the relative proportions of the three arms in the German IInd Army were as follows: cavalry to infantry as 1:8; and 3.4 guns per 1,000 men. The proportion between the two principal arms in the IIIrd Army Corps of the German army, at the outbreak of the Franco-German war, was as 1:18.8; on the first day of the battle of Le Mans it was as 1:16.6; at the opening of the campaign there were 4.6 guns per 1,000 men, at the close of the campaign 5.8 guns per 1,000 men. This was still more marked in the Ist Bavarian Army Corps, which, on October 31st, had 5.8 guns and on December 9th even 11.1 guns per 1,000 men. At present Germany has approximately 6, and France 3.63 guns per 1,000 infantry. The manner in which infantry fights imprints its distinguishing mark on the tactics of an entire period; thus, according to the combat formations of infantry, we may speak of a period of “linear,” “column,” and “extended order” tactics. Infantry can be equipped more cheaply and trained more quickly than the other arms. In July, 1870, the French army consisted of 116 infantry regiments and 21 rifle battalions, but 38 rifle battalions were raised in addition to a large number of regiments of _gardes mobiles_ and volunteers. Infantry is as well adapted for combat with firearms as for combat with the bayonet, for attack as for defense, for action in close as in extended order. It can fight on any terrain which is at all passable, and is more independent of weather and seasons than the other arms; it surpasses the other arms in endurance, a man, on account of his will power, bearing privations and exertions better than a horse. On the other hand, the losses suffered by foot troops in action and through exertions on the march are greater than those of the mounted arms.[25] [25] Percentages of cases of sickness in the campaign 1870/71: Infantry: 69.8; Field Officers: 13.26; Captains: 10.19; Lieutenants: 3.85% Artillery: 57.7; „ „ 4.04; „ 4.84; Lieutenants: 4.52„ Cavalry: 37.5; „ „ 5.61; „ 2.29; Lieutenants: 3.24„