“…While Small's interest was in studying learning, Kline's attention was at first attracted by the "food-box-finding" capacity of rats which, being gnawers, had to be studied "under the hunger impulse, free from fear, and, as far as possible, under natural conditions" [25]. In fact, in the conviction that the natural method and the experimental one "are necessary to a more abundant ingathering of facts" [28], he adopted an epistemological approach to the research on animals' learning that ranged from careful and continuous observations of naturally occurring behaviours to laboratory experimental observations involving mazes which, however, would inhibit the animals' ability to act freely. The idea for the second approach came from his 1897 research on chicks' "sickness for home", which involved reading Association in Animals, a chapter of Morgan's Introduction to Comparative Psychology, where the author explained the use of little boxes similar to traps to study the ways in which rats searched for food in out-of-the-way places, and observing an investigation conducted in 1897 in the Department of Biology at Clark by Colin C. Stewart, whose "methods, apparatus, and techniques were both interesting and instructive and made a decided impression" upon Kline.…”