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A quantitative study has been made of the relationship between Moniliformis dubius and Periplaneta americana.1. Eggs removed from the body cavity of the worm hatch at a higher rate after dessication and after a short period of time following removal.2. There is an exponential decline in the additional number of cystacanths recovered as the dose is increased linearly.3. Female cockroaches are more susceptible to high levels of infection than males.4. Direct injection into the haemocoele produces a similar recovery rate to that from oral infection.5. Previous infection does not seem to affect the success of a superimposed infection.6. Rates of development and growth are described.7. The effect of the parasite on the concentration of free amino acids in the haemolymph was found to be negligible.I would like to thank Miss S. Arnold and Mr D. Barnard for technical assistance, Mr E. Walters for help with statistical analysis, Dr D. W. T. Crompton for many helpful discussions and Dr P. J. Whitfield for reading this paper. This work has been carried out during the tenure of a Science Research Council Studentship.

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The Iocomotory behavior of human blood neutrophil leukocytes was studied at a boundary between two surfaces with different chemokinetic properties. This was achieved by time-lapse cinematography of neutrophils moving on coverslips coated with BSA, then partcoated with immune complexes by adding anti-BSA IgG with a straight-line boundary between the BSA and the immune complexes. Cell locomotion was filmed in microscopic fields bisected by the boundary, and kinetic behavior was assessed by comparing speed (orthokinesis), turning behavior (klinokinesis), and the rate of diffusion of the cells on each side of the boundary, using a recently described mathematical analysis of kinesis. In the absence of serum or complement, the proportion of motile cells and their speed and rate of diffusion were greater on BSA than on antiBSA, but there was no consistent difference in turning behavior between cells on the two surfaces. The immune complexes were therefore negatively chemokinetic in comparison with BSA, and this resulted from a negative orthokinesis with little or no contribution from klinokinesis. As would be predicted theoretically, this resulted in gradual accumulation of cells on the immune complexes even in the absence of a chemotactic factor. In further studies, a parallel plate flow chamber was used to show that, under conditions of flow, neutrophils accumulated much more rapidly on a surface coated with BSA-anti-BSA than on BSA alone. Moreover, neutrophils on immune complex-coated surfaces lost their ability to form rosettes with IgG-coated erythrocytes. This suggests that neutrophils on immune complex-coated surfaces redistribute their Fc receptors (RFcT) to the under surface, and that the lowered speed of locomotion is due to tethering of neutrophils by substratum-bound IgGFc.