No abstract

Previous data suggest that liver glutathione (GSH) serves as a cyst(e)ine reservoir in rats starved or fed cyst(e)ine-deficient diets. In the present study we investigated whether extrahepatic tissue GSH concentrations also decreased during cystine (Cys-Cys) depletion and whether excess dietary cystine increased tissue GSH and cysteine (Cys) concentrations. Five groups of growing rats (80-100 g) were fed diets containing crystalline L-amino acids differing in methionine (Met) and cystine (Cys-Cys) content for 15 days. All diets were isonitrogenous (1.3 g/100 g diet) and provided the minimum Met (0.17%) required by growing rats. Diet 1 provided 0.17% Met and 0% Cys-Cys, diet 2 (the recommended diet) provided 0.17% Met and 0.26% Cys-Cys, diet 3 provided 0.50% Met and 0% Cys-Cys, diet 4 provided 0.17% Met and 0.39% Cys-Cys and diet 5 provided 0.17% Met and 0.52% Cys-Cys. Diets 2 and 3 were isosulfurous at 3.3 mmol/100 g diet. Diets 4 and 5 provided 50 and 100%, respectively, more Cys-Cys than required when 0.17% Met was present. Animals fed diet 1 (Cys-Cys depletion) had significantly decreased (P less than 0.05) liver, muscle, spleen, heart and thymus GSH concentrations, whereas brain, small intestine and erythrocyte GSH concentrations remained unchanged. Although brain and small intestine Cys concentrations were not affected by Cys-Cys depletion, spleen, heart and liver Cys concentrations decreased significantly (P less than 0.05). Feeding Cys-Cys above the requirement level did not increase GSH and Cys concentrations of any tissue except liver where Cys levels were elevated. The data indicate that liver, muscle, spleen, heart and thymus GSH serve as Cys reservoirs during Cys-Cys depletion.

An analysis of 1324 accidents over a 42-month period at a university day care center revealed that toddlers had the highest average number of injuries, most of them self-induced, that accidents peaked in mid-morning, and that September was the month with the highest accident rate. Although accidents were frequent, injuries were minor. Results are contrasted to those of earlier studies.

The new science programs for the secondary school assume the importance of the laboratory as a means for students to gain greater understanding of and experience with ~cience.l-~ The relative effectiveness of laboratory and demonstration approaches was a popular research area during the 1 9 3 0 '~.~-~ Most of these studies failed to establish that the laboratory approach was superior to the teacher demonstration procedure. As a result the laboratory was deemphasized, especially in general education science courses during the 1940's. However, achievement tests were the only measures used to determine the outcomes of instruction. These tests were largely contentcentered where there was a premium placed upon mastery of information.With the great interest in science instruction and science courses following World War I1 caused by the harnessing of nuclear power and the space race, the laboratory in the secondary school appeared once more as a central feature of the traditional science offerings. To practicing scientists and to well-trained, modern, and reflective science teachers, the laboratory is considered to be of central importance in characterizing science. In the national programs of evaluation that have been conducted it appears that research workers have ignored a basic question concerning the effects of the laboratory upon learning science.Two recent studies conducted by two independent investigators have produced conflicting results. Coulter reports little significant difference in use of laboratory when compared to teacher demonstrations in biology instruction.1° In this case the course of study and the same teacher were involved. I n a much larger study conducted by Sorenson 20 sections of biology students were studied.ll Ten sections experienced a lecture approach and ten a laboratory approach. Sixteen teachers were involved. The laboratory group displayed significantly greater growth in terms of critical thinking and understanding science and greater change in dogmatism. The lack of control of the teacher variable leaves the design of this study in question, especially in view of recent reports by Yager.lz' l 3 In a study appearing in 1947, Mallinson reports no difference in terms of achievement in general biology when two groups experienced the laboratory and a lecturedemonstration approach, re~pective1y.l~ Mallinson called for more research utilizing more careful controls. This study attempts to incorporate into the design the necessary controls. The ProblemWhat are the relative differences and the specific outcomes of instruction when secondary students study biology with a discussion approach only (called nonlaboratory group) with a discussion-demonstra-76

A total of 53 high‐ability students who had completed the eleventh year in high school enrolled in a standard college chemistry course at the University of Iowa. Half of them had completed a high‐school course in chemistry and half had not. After 2 months of instruction during a summer session, there was no difference between groups as to attitude toward chemistry, performance on the ACS‐NSTA Chemistry Achievement Examination, final examination for the course, and course grade. There was a great difference in the amount of time required of tutors; the students who had not completed high‐school chemistry spent more time in studying and with tutors.