Volume IV of the Oeuvres de Pasteur (Masson), collecting Pasteur's studies on the silkworm diseases pébrine (corpuscle disease) and flacherie, carried out around Alais in the 1860s and 1870s. It covers the physical signs of disease, the history of earlier research, the nature and contagion of the corpuscles, and Pasteur's method of cellular grainage (microscopic selection of healthy moths for egg production). It also covers the hereditary and contagious character of flacherie, historical notes on sericulture, and appended official reports, letters and Senate discussions confirming the method. Illustrated with microscope plates, photographs and engravings of silkworms and rearing practice, and many tables of corpuscle counts.