John gradually became led into the study of comparative anatomy, from finding that structures which were complex in the human subject were simpler in animals, or different in plan, in both cases throwing light on human anatomy and physiology. Thus he made dissections of all the commoner animals, and always preserved the parts which interested him. He soon passed beyond the ordinary range, and made acquaintance with the keeper of the Tower menagerie, that he might obtain the bodies of such animals as died there. Similarly he even would purchase animals when alive, from travelling showmen, simply requiring them to bring him their bodies whenever they happened to die. He bought all rare animals that came in his way: others were presented to him by friends, and thus an ample supply of material was secured. There is some obscurity about the reasons which induced the younger brother in 1760 to accept an appointment as staff-surgeon in the army, joining the expedition to Belleisle in 1761. There is not much doubt, however, that his health had suffered, and that a foreign voyage and residence were calculated to restore him. In 1762 he was employed with the army in Portugal, and in this experience laid the foundation of his knowledge of military surgery. During this expedition he neglected no opportunity of forwarding his studies in comparative anatomy and physiology. Thus when at Belleisle, in order to discover whether animals in a state of hibernation could digest food, he introduced worms and pieces of meat into the stomachs of lizards, and kept them under observation in a cool place. He found the substances so introduced remained perfectly undigested. So in 1762, near Lisbon, he tested the hearing of fishes by observing the effect of the report of a gun upon the inhabitants of a nobleman’s fish-pond.