THE VALUE OF VEGETABLE EXTRACTS IN CULTURE MEDIUMS

Abstract

It was found that as little as 0.01 cc. of aqueous extracts of potato, carrot, spinach, radish or beef heart sterilized by filtration, when added to 6-7 cc. of nutrient broth, promoted growth of many streptococci not growing in broth alone; 0.2 cc. was sufficient to give vigorous growth of most streptococci. Potato extract was found most satisfactory, because of its high nutritive value and keeping qualities. Heat was found to have an effect on the extract proportional to precipitation, media giving most precipitate being least useful in accelerating growth. Either proteid or non-proteid N fractions of potato extract serve to stimulate growth of streptococci, but not to as marked a degree as whole extract. Potato extract may be used in place of fresh blood in many instances where it is not essential to observe hemolysis. It is helpful in getting a growth of streptococci and pneumococci free from cells and precipitated fractions of medium. As an enriching substance in ordinary fermentation tubes it allows growth of streptococci without interfering with the action on the sugar. The material in potato extract responsible for promoting growth is thought to be nitrogenous, furnishing suitable food rather than food-assessory substances.