INCUBATION

The classification of the genus Proteus is still to some extent controversial, although recent investi-gations have clarified the position considerably. The basis of the modern work was the demonstration by Moltke (1927) that 194 Proteus strains all rapidly hydrolysed urea. For the purposes of this paper, the genus Proteus includes all motile, Gram-negative, straight rods which do not ferment lactose, do ferment glucose, and hydrolyse urea rapidly. (With a stab culture in a solid urea-containing medium a positive result is obtained in less than four hours.) On such a basis, Rustigian and Stuart (1943) proposed to include in the genus four species: P. vulgaris, P. mirabilis, P. morgani, * and P. rettgeri, which can be readily differentiated on the basis of a few simple biochemical reactions. Cook (1948) studied the cultural characteristics of the genus more fully and showed the relative frequency of the four species. For the purposes of routine identification it is justifiable to determine the species on the basis of three characteristics only; sucrose fermentation in 24 hours, mannitol fermentation, and indole production, as shown in Table I