W. H. Peterson

The Relation Between the Number of Bacteria and Acid Production in the Fermentation of Xylose

The study of the rate of growth of bacteria and the extent of the changes in the composition of the nutrient medium which accompany growth has engaged the attention of bacteriologists for many years. The most important contributions to this problem may be divided along two lines: first, the relation between the number of bacteria and the amount of the end products at different times; second, involved mathematical equations and formulae to explain the rate of multiplication of bacteria in nutrient solutions. The usual method of investigation is to seed a small number of bacteria into a suitable medium under known conditions, and after given intervals of time to estimate the number by the plate method. The rate of development can be obtained for many kinds of bacteria by measuring their products, i. e.,* the extent of fermentation is assumed to be proportional to the number of bacteria that have developed. This article is primarily concerned with the rate at which byproducts are formed and their relation to the number of bacteria. In order to study the mechanism of fermentation reactions, the rate of development of the micro-organism is of importance. At present, observations are not available which cover the whole period of growth from commencement of seeding to the period when growth ceases altogether, and by-products are no longer formed. It is true that there are ample observations available on the reproduction of bacteria and yeasts in the early stages of growth.