External biliary fistula.

External biliary fistulas, once common, are now rare: before the present report of 4 cases only 27 cases have been reported in the English literature since 1900. Review of the records of four patients with external biliary fistula confirmed its occurrence in patients over 50 years of age and the variable site for operning of the fistulous tract. Cholecystectomy provided successful treatment in three of the four patients but the fourth was too ill to undergo an operation; in general, definitive treatment is cholecystectomy, together with excision of the fistulous tract if this takes a direct path through the abdominal wall from the gallbladder, or curettage if the course is devious.     

Abortive Infection of Shigella dysenteriae P2 by T2 Bacteriophage

We have investigated some of the biochemical events that accompany the abortive infection by T2 of Shigella dysenteriae lysogenized with the temperate phage P2. After infection with T2, protein and RNA synthesis continued for 3 to 5 min. The virus-induced enzyme, deoxycytidylate hydroxymethylase was produced in reduced amounts (15% of normal), and the extent of deoxyribonucleic acid (DNA) synthesis was 0.1% of that found with a nonlysogenic strain. Measurements of the production of acid-soluble fragments and sedimentation analyses failed to detect enzymatic degradation of the infecting viral DNA which could be specifically related to the presence of the prophage P2. Each interaction between T2 and a bacterium resulted in the death of the cell. This observation is consistent with results obtained with other types of bacteria which show that only when a nucleolytic attack occurs on T2 DNA does the cell have an increased capacity to survive after adsorption of T2.     

Dental bacterial plaque

The literature on the subject of dental bacterial plaque is extensive. In spite of considerable research, the mode of its formation together with the variability in bacterial content requires further clarification. Mechanical methods of plaque control are effective but limited in a population sense. Of the numerous chemotherapeutic agents in plaque control, chlorhexidin appears the most effective.