Properties of behavior under different random ratio and random interval schedules: A parametric study.

Four pigeons were trained to peck a key under different values of a temporally defined independent variable (T) and different probabilities of reinforcement (p). Parameter T is a fixed repeating time cycle and p the probability of reinforcement for the first response of each cycle T. Two dependent variables were used: mean response rate and mean postreinforcement pause. For all values of p a critical value for the independent variable T was found (T=1 sec) in which marked changes took place in response rate and postreinforcement pauses. Behavior typical of random ratio schedules was obtained at T 1 sec and behavior typical of random interval schedules at T 1 sec.

An outbreak of diphtheria in a hospital for the mentally subnormal.

An account is given of two separate outbreaks of diphtheria amongst mentally subnormal patients and nursing staff. In a total hospital population of about 1000 the number of people involved as carriers or cases was 60 and there were five deaths. The 60 people comprised 56 patients, of whom four were involved in both outbreaks, and four nurses. The organisms isolated were C. diphtheriae mitis but five strains were non-toxigenic. It is postulated that the outbreak began following the conversion of a non-toxigenic organism to a toxigenic one by bacteriophage action. The fatal cases were examples of membranous pharyngo-laryngo-tracheo-bronchial diphtheria with well marked pseudo-casts of the upper air passages.