In previous papers it has been shown that unheated plant tissue, in the form of potato, contains the two factors necessary for the growth of organisms of the hemoglobinophilic group. Further studies (5) confirmed these findings and showed that yellow and white turnip, carrot, beet, parsnip, and sweet potato can replace blood in the cultivation of Bacillus influenzæ.
In the present paper it has been shown that vegetable tissues also greatly facilitate and stimulate the growth of other organisms entirely unrelated to Bacillus influenzæ. Three varieties of Gram-positive cocci have been used in the present study, pneumococcus, Streptococcus hamolyticus, and Streptococcus viridans. With pneumococcus it has been previously shown that prompt and luxuriant growth will occur in broth containing unheated potato even though the seeding be so small that no growth whatever will occur with the same seeding in plain broth (5). In the present study it has been shown that even in dextrose broth this minimal inoculation is followed by a prolonged period of lag, whereas in potato broth this same inoculum serves to initiate immediate and rapid growth. When pneumococci are grown in potato broth not only is the period of lag abolished, but the stationary period of growth is extended and cell death is delayed. Moreover, in plant tissue medium the zone of hydrogen ion concentration within which growth of pneumococcus can be initiated is considerably extended beyond the acid and alkaline limits of the optimal range in ordinary bouillon.
It has been found also that the presence of unheated plant tissue in the media likewise stimulates growth of hemolytic and non-hemolytic streptococci.
In this investigation no attempt has been made to determine the exact nature of the substances in plant tissue upon which these properties depend. That they are not of the nature of readily fermentable carbohydrates, however, is made evident by the fact that no increased production of acid occurs in the pneumococcus culture when potato is present.