42 BIOLOGY OF PNEUMOCOCCUS 



and sustain growth of Pneumococcus in otherwise unsuitable me- 

 dia. Robertson, Sia, and Wood 1149 ascertained that the protective 

 action of gelatin lies largely in shielding pneumococci against 

 physical injury — possibly the toxic action of electrolytes — which 

 occurs during dilution in solutions of crystalloids. Furthermore, 

 gelatin exerts a well-marked preservative action of unknown na- 

 ture in protecting the organisms against early dissolution. 



One of the most commonly used substances is blood, of either 

 man, rabbit, horse, or sheep. Pasteur, Sternberg, and Levy and 

 Steinmetz 802 early recognized its value. Citrated, laked, or, better, 

 defibrinated blood augments the growth-promoting value of the 

 substrate. It is best used in a ratio of one part or less to ten to 

 twenty parts of medium. Normal serum, transudates, and ascitic 

 and hydrocele fluids similarly supply elements favorable to the 

 growth of Pneumococcus, and are common ingredients in many 

 media formulas (Fraenkel, 468 Behring and Nissen, 98 Mosny, 933 Le- 

 vinthal, 800 and many others). 



In a study of the growth-promoting properties of serum from a 

 variety of animal species, Bezancon and Griffon 112 found that, in 

 general, growth was more rapid and abundant in the serum of ani- 

 mals susceptible to pneumococcal infection. However, in these se- 

 rums cell death took place rapidly after maximal growth had been 

 reached. In the serum of resistant animals, on the other hand, 

 growth was meager, although the organisms remained viable and 

 virulent for a longer period of time. The serum of young animals, 

 whether of a sensitive or refractory species, possessed the growth- 

 promoting properties of susceptible species, whereas the serum of 

 older animals was less favorable to growth. 



Bordet 139 has recently described an unexplained and as yet un- 

 confirmed cultural and morphological appearance of cultures in 

 rabbit serum. The growth of pneumococci had a milky appear- 

 ance, and at the bottom of the tube a sediment formed which con- 

 sisted of a clustered mass of large round elements. These bodies 

 failed to take well the basic stains but were readily stained by neu- 



