The aim of this systematic literature review is to map the longitudinal research in the field of Internet Use (IU) and Problematic Internet Use (PIU) in adolescents and emergent adults. Further, this study endeavours to examine the terminology and instruments utilized in longitudinal IU and PIU research and investigate whether statistically significant results have arisen from the areas of research focus. In a total of 29 studies, trends in the research of adolescent/emergent adult IU and PIU were discovered. These trends were conceptualized into individual, contextual and activity-related factors. Findings suggested that individual factors are the most researched and have demonstrated significant relationships with adolescent/young adult PIU. However, more research on contextual and activity-related factors is needed in order to achieve a clearer understanding of young people's IU and PIU behaviours, and to incorporate into a comprehensive model that will guide future research in this growing field.

SUMMARYThe phage-typing scheme of Callow (1959) has been extended. The original number of types was 34; this has now risen to 207. Tables are presented which show the provisional type designations and the definitive designations now being introduced.

Berry, L. Joe (Bryn Mawr College, Bryn Mawr, Pa.), Dorothy S. Smythe, and Louise S. Colwell. Inhibition of inducible liver enzymes by endotoxin and actinomycin D. J. Bacteriol. 92:107-115. 1966.-Bacterial endotoxin at the ld(50) level lowers liver tryptophan pyrrolase in mice, it prevents for 16 to 20 hr the induction of the enzyme by a concurrent injection of cortisone, it lowers significantly but does not prevent substrate induction, and it reduces the enzymatic activity promptly and significantly when administered during the course of hormonal induction. The ld(50) amount of actinomycin D has a similar effect on tryptophan pyrrolase, except that its inhibition of induction by cortisone persists for a longer period of time. Endotoxin in the intact mouse induces tyrosine-alpha-ketoglutarate transaminase almost as well as cortisone, but not in the adrenalectomized animal, a fact that suggests induction of this enzyme is due to release of endogenous adrenal hormones. Actinomycin D, on the other hand, has an effect on this transaminase similar to that on tryptophan pyrrolase. The site of action of endotoxin and actinomycin D would appear to be similar for one of the two enzymes studied and different for the other, a relationship that requires a specificity difficult to imagine for a material as complex as endotoxin.

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THE epidemiological value of different methods of distinguishing types within a bacterial species depends on their discriminating ability, reliability and ease of performance. Discriminating ability depends primarily on the number of types distinguished, but is poor if a large proportion of strains falls into a single type. Reliability depends on the reproducibility of each isolate's results in repeated tests and on the stability of the typing characters among different isolates from the same epidemic episode.Probably the best single method for differentiating types in Salmonella typhimurium is the phage-typing system of Callow (1943, 1951) , 1972). This method is less discriminating and more laborious than phage-typing, but it distinguishes different biotypes within individual phage-types, so that its combination with phage-typing gives a finer discrimination than either method alone (Kallings and Laurell, 1957;Rische and Kretzschmar, 1962;Lewis and Stocker, 1971).In a combined phage-typing and biotyping study of S. typhimurium we found some serious defects in the Kristensen scheme.(1) The fermentation tests with d-, Z-and rn-tartaric acids and citric acid proved unreliable and often gave different results on different occasions of testing the same isolate. Improved, more reliable methods were developed for the tartaric acids by Alfredsson et al.(1972) and these methods are used in the new scheme described in the present paper.(2) In our series of strains, both the original and the modified tests identified several biotypes with patterns of reactions different from those of the twenty-one types already recognised, but the new types could not be accommodated in the Kristensen classification in such a way as to show their relations to the existing types. For example, a group of strains designated " type 19Xd " by Morgenroth and Duguid (1968) resembled biotype 6 except that it was rhamnose negative; if this new type had been added to the scheme as type 22, its close relation to typ6 6 would not have been apparent. (3) We found that discrimination in biotyping could be improved by the addition of tests for the fermentation of trehalose in peptone water, fermentation of rhamnose in Bitter's medium, fermentation of inositol at 25"C, gas production from glucose, growthfactor requirements and presence of flagella and fimbriae, but the results of these extra tests could not be shown in any convenient way within the Kristensen classification. Mutational fermentation. Alfredsson et al. (1972)found that a major cause of unreliability in tests with the tartaric acids was the power of many non-fermenting strains to produce ~ ~~