As regards the _material_, a distinction is drawn between the treatment of the material of mobile medical units, of fixed medical establishments, and of material belonging to Voluntary Aid Societies. (_a_) Mobile medical units which fall into the hands of the enemy must not be deprived of their material, including their teams, whatever may be the means of transport and whoever may be the drivers employed (article 14). The competent military authority is, however, permitted to make use of the material in captured medical units for the treatment of the wounded and the sick at hand, provided it is restored under the same conditions, and so far as possible at the same time, as laid down for the release of the medical personnel by article 12. (_b_) The buildings and material of fixed medical establishments which, because the locality where they are is militarily occupied, fall into the hands of the enemy, remain, according to article 15, "subject to the laws of war," that means they remain entirely in the power of the captor, but they may not be diverted from their medical purpose so long as they are necessary for the proper treatment of the wounded and the sick. Should, however, urgent military necessity demand it, a commander may dispose of them, provided he makes previous arrangements for the welfare of the wounded and sick found in the fixed establishments. (_c_) The material of Voluntary Aid Societies, which are duly recognised, is, according to article 16, considered private property and must, therefore, be respected as such under all circumstances, although it may be requisitioned. [Sidenote: Personnel.] § 121. The personnel engaged exclusively in the collection, transport, and treatment of the wounded and sick, as well as in the administration of mobile medical units and establishments, the chaplains attached to armies, and, lastly, pickets and sentinels guarding medical units and establishments, must, according to article 9, under all circumstances be respected and protected. If they fall into the hands of the enemy they must not be treated as prisoners of war. According to article 12, however, they are not free to act or move without let or hindrance, for, if their assistance is indispensable, they may be called upon by the captor to carry on their duties to the wounded and the sick. But when their assistance is no longer indispensable, they must be sent back to their army or to their country at such time and by such route as may be compatible with military exigencies, and they must be allowed to take with them such effects, instruments, arms, and horses as are their private property. So long as they are detained by the enemy he must, according to article 13, grant them the same allowances and the same pay as are due to the personnel holding the same rank in his own army.