I n the earliest notations on bacterial there was great interest in morphological response to environment Temperature shifts and moisture restriction changed a bacterium into a still prop agating but unrecognizable form . It was demonstrated that virulence and configuration were syn chronized; sometimes pleomorphism signaled loss of virulence, sometimes an increase. Therefore, the experimentalists sought an explanation of seasonal disease and of epidemics in microbial response to annual modifications in soil and waters . Whether microbial variations and mutations occur predominantly in animal hosts or in air, soil, or water remains to be determined. The dependable seasonal variations in enteric and respiratory infections remain enigmatic to this day. The effects of sunlight, temperature, and nutrition upon the bacterial wall , and hence upon its morphology, are studied largely in laboratory-created environments , as described below.