CULTIVATION OF BACTERIA. 187 



action is first determined enlture-niedia are more often acid than 

 alkaline, it is proposed that acid media be designated by the plus 

 sign and alkaline media by the minus sign, and that the degree 

 of acidity or alkalinity be noted in parts per hundred. Thus, a 

 medium marked + 1.5 would indicate that the medium was acid, 



and that 1.5 per cent, of - sodium hydroxid is required to make 



it neutral to phenolphthalein ; while — 1.5 would indicate that 



the medium was alkaline and that 1.5 per cent, of - acid must be 



added to make it neutral to the indicator." 



" Standard reaction of media ( provisional) : 



" Experience seems to vary somewhat as to the optimum degree 

 of reaction which shall be uniformly adopted in the preparation 

 of standard culture-media. To what extent this is due to varia- 

 tion in natural conditions as compared with variations of labora- 

 tory procedure, it seems impossible to state. Somewhat different 

 degrees of reaction for optimum growth are required, not only in 

 or upon the media of different composition and by bacteria of 

 different species, but also by bacteria of the same species when in 

 different stages of vitality. The bulk of available evidence from 

 both Europe and America points to a reaction of + 1.5 as the opti- 

 mum degree of reaction for bacterial development in inoculated 

 culture-media. While this experience is at variance with that in 

 several of our own laboratories, it has been deemed wisest to adopt 

 •+ 1.5 as the provisional standard reaction of media, but with the 

 recommendation that the optimum growth reaction be always 

 recorded with the species." 



Bouillon is one of the most useful and most simple of 

 the media. Its preparation is as follows : To 500 grams 

 of finely-chopped lean, boneless beef, 1000 c.cm. of clean 

 water are added and allowed to stand for about twelve 

 hours on ice. At the end of this time the liquor is de- 

 canted, that remaining on the meat expressed through a 

 cloth, and then, as the entire quantity is seldom regained, 

 enough water added to bring the total amount up to 1000 

 c.cm. This liquid is called the meat-infusion. To it 10 

 grams of Witte's or Fairchild's dried beef-peptone and 5 

 grams of sodium chlorid are added, and the whole boiled 

 until the albumins coagulate. Smith * says that when 

 the peptones are added before boiling most of them are 

 lost, and therefore recommends that the meat-infusion be 



1 Trans. Assoc. Amer. Phys., 1896. 



