44 BIOLOGY OF PNEUMOCOCCUS 



peptone broth or Martin bouillon gives early growth with less pro- 

 duction of acid than that which occurs when glucose is used. In 

 such a medium it is probably the glycogen or other sugars which 

 supply the stimulus, while the tissue itself and the hemoglobin fur- 

 nish the other growth-promoting factors. The protective action of 

 muscle tissue is exemplified in the hormone-blood agar and hor- 

 mone-gelatin broth of Bailey. 67 The formula is a modification of 

 that of Huntoon 684 for the preparation of original hormone me- 

 dium, and both methods, and also that of Douglas for making 

 tryptic digest medium, yield substrates well suited not only for the 

 prolific growth of pneumococci but for conservation of essential 

 biological characters of the organism. 



Still another factor to be considered is the oxygen requirement 

 of Pneumococcus. The organism is a facultative anaerobe, and 

 grows both in the presence and absence of oxygen. Examples of 

 anaerobic strains of pneumococci have been encountered by Avery 

 and his associates,* while two similar strains which apparently 

 constitute two new serological types have recently been described 

 by Smith. 1296 Because of its action in elaborating toxic peroxides 

 in the surrounding medium, as first demonstrated by McLeod and 

 Glovenlock 885 and later proved by McLeod and Gordon 881 " 4 to be 

 hydrogen peroxide, Pneumococcus may hinder or entirely prevent 

 its own growth. The inhibiting effect of the peroxide may be over- 

 come by the addition of plant tissues or other substances exerting 

 an oxidizing- reducing action (Avery and Morgan 62 ). 



VEGETABLE ACCESSORY SUBSTANCES 



Avery and Morgan 61 ' 63 found that the addition to broth of ster- 

 ile, unheated plant tissue, such as yellow and white turnip, carrot, 

 beet, parsnip, white and sweet potato, and banana,f not only 

 caused acceleration of pneumococcal growth, but served to induce 

 abundant multiplication even when the seeding was too minute to 



* Personal communication. 



f Falk, Valentine, McGuire, and Whitneysss have more recently (1932) rec- 

 ommended the use of the green banana as enriching material in the place of 



