The Influence of the Substrate on the Action of Drugs

During the last few years, a considerable amount of work has been done on the hydrogen ion concentration of the blood in health and disease, as well as on its influence on the rate of multiplication of bacteria in artificial media. Whilst working in Dr. H. H. Dale's laboratory I noticed whilst testing the action of the cinchona alkaloids on Paramecium caudatum. that this ciliate was easily destroyed in the afternoon, whilst in the morning it appeared to be quinineresistant. In order to avoid contaminating the stock culture, it was my practice to take up 50 c.c. of the stock and place it in a sterile Petri dish, and from this volume carry out the whole of the experiments for the day. At 10 o'clock in the morning a 1-10,000 dilution was necessary to kill these ciliates, whilst at 2 o'clock a dilution of