Utilizing the amphoteric nature of most sulfonamides, a simple extraction method followed by the colorimetric development, based on the diazotization-coupling reaction with N-(l-naphthyl) ethylenediamine dihydrochloride, is described for the determination of sulfonamides alone and in combination with procaine penicillin G in milk. Recoveries for the ten sulfonamides studied ranged from 81 to 100% recovery at the 100-p.p.b. level.

In a counterbalanced design, 16 rats were alternately tested for container neophobia and preference for earned food. Testing for earned food preference was conducted after three exposures to the free food source followed by seven exposures to the earned food source in an operant conditioning chamber. Testing for container neophobia was conducted in home cages after 21 sessions of habituation to a familiar container. There was a significant positive correlation between preference for earned food and container neophobia.A number of researchers have reported that under certain conditions, rats will press a lever for food in the presence of free food (see D'Amato, 1974, for a review). Some authors (Carder & Berkowitz, 1970;Jensen, 1963;Singh, 1970) have suggested that rats have a "preference" for earned food, while others (Atnip & Hothersall, 1973;Taylor, 1972) have found that "preference" for earned food is limited to a small subset of the rat population. These latter authors suggest that though rats generally do not prefer earned to free food, the question as to why some rats will continue to leverpress for food when identical food, requiring less effort, is available has yet to be answered. Recently, Mitchell, Scott, and Williams (1973) suggested that neophobia is the essential factor generating a propensity for earned food in rats. In this view, it is not the method of procurement, as suggested by previous authors (Carder & Berkowitz, 1970;Davidson, 1971;Jensen, 1963), but rather the animal's familiarity with the different food sources that determines its behavior in the earned food paradigm. The present experiment examines this relationship between a rat's neophobic avoidance of a novel food source and its preference for earned food. METHOD SubjectsSixteen naive male Long-Evans rats, approximately 210 days old, served as Ss. All Ss were individually housed in 24 x 17.4 x 18.5 em stainless steel cages with water freely available. ApparatusFor the· portion of the experiment dealing with earned food preference, two identical operant conditioning chambers more fully described by Mitchell et al (1973) were used. Briefly, the chambers were enclosed in two separate sound-attenuating enclosures and dispensed earned food into a brass hopper by *This research was supported by National Science Foundation Grant GB-40314 awarded to Robert C. Bolles, whom we thank for his support. We also thank D. Winfield Scott for his technical assistance and Stephen C. Woods and Ron Sigmundi for their helpful comments on the manuscript. Requests for reprints should be addressed to Denis Mitchell, Department of Psychology, University of Washington, Seattle, Washington 98195. This paper was sponsored by Stephen C. Woods, who takes full editorial responsibility for its contents. 182means of a response lever requiring a force of 0.20 g to operate. One-way mirrors permitted unobtrusive viewing of Ss in the chambers. Both free and earned food consisted of 0.045-g Noyes pellets. Earned pellets were provided on a continuous reinforcement schedu...