This paper by Stephen Boyden describes an in vitro technique for assessing the chemotactic activity of soluble substances on motile cells, specifically rabbit polymorphonuclear leucocytes. The method involves using a perspex chamber with a filter membrane to separate two compartments, allowing leucocytes to migrate towards a solution of the substance being tested. The study focuses on the chemotactic effect of antibody-antigen mixtures, particularly in the presence of fresh normal rabbit serum. Key findings include: 1. **Chemotactic Activity of Soluble Substances**: Soluble substances, such as human serum albumin (H.S.A.) and ovalbumin, generally show weak or no chemotactic activity in normal serum but become strongly active when mixed with specific antiserum. 2. **Effect of Antigen Concentration**: Optimal chemotactic activity is achieved at a specific concentration of antigen relative to antibody. 3. **Supernatants and Precipitates**: Supernatants from antibody-antigen mixtures, even after centrifugation, retain significant chemotactic activity. The chemotactic effect is not due to the specific precipitate but to substances in solution. 4. **Inactivation of Antibody-Antigen Mixtures**: Inactivated antibody-antigen mixtures do not exhibit chemotactic activity, suggesting that the chemotactic substance is heat-labile. 5. **Heat-Stable Chemotactic Substance**: The interaction of antibody and antigen at 37°C produces a heat-stable chemotactic substance that acts directly on leucocytes. This substance is not produced when the mixture is inactivated before incubation. The study suggests that the chemotactic response involves the formation of a complex between antibody and antigen, which interacts with a heat-labile substance (possibly an enzyme or complement component) to produce a heat-stable chemotactic agent. This mechanism may explain the chemotactic effects of various bacterial and plant products on leucocytes and could have implications for understanding immune responses and specific acquired resistance to microbial infections.This paper by Stephen Boyden describes an in vitro technique for assessing the chemotactic activity of soluble substances on motile cells, specifically rabbit polymorphonuclear leucocytes. The method involves using a perspex chamber with a filter membrane to separate two compartments, allowing leucocytes to migrate towards a solution of the substance being tested. The study focuses on the chemotactic effect of antibody-antigen mixtures, particularly in the presence of fresh normal rabbit serum. Key findings include: 1. **Chemotactic Activity of Soluble Substances**: Soluble substances, such as human serum albumin (H.S.A.) and ovalbumin, generally show weak or no chemotactic activity in normal serum but become strongly active when mixed with specific antiserum. 2. **Effect of Antigen Concentration**: Optimal chemotactic activity is achieved at a specific concentration of antigen relative to antibody. 3. **Supernatants and Precipitates**: Supernatants from antibody-antigen mixtures, even after centrifugation, retain significant chemotactic activity. The chemotactic effect is not due to the specific precipitate but to substances in solution. 4. **Inactivation of Antibody-Antigen Mixtures**: Inactivated antibody-antigen mixtures do not exhibit chemotactic activity, suggesting that the chemotactic substance is heat-labile. 5. **Heat-Stable Chemotactic Substance**: The interaction of antibody and antigen at 37°C produces a heat-stable chemotactic substance that acts directly on leucocytes. This substance is not produced when the mixture is inactivated before incubation. The study suggests that the chemotactic response involves the formation of a complex between antibody and antigen, which interacts with a heat-labile substance (possibly an enzyme or complement component) to produce a heat-stable chemotactic agent. This mechanism may explain the chemotactic effects of various bacterial and plant products on leucocytes and could have implications for understanding immune responses and specific acquired resistance to microbial infections.