36 CONDITIONS OF BACTERIAL LIFE. 



gelatin (and agar) a medium which contains just so much 

 sodium hydroxid as is required to produce a minimum 

 reddening of phenolphthalein. All the plates in this atlas 

 are prepared with the use of such nutrient media for such 

 cultures. This was done after the investigation of five 

 important bacteria had indicated to us that additions of 

 acids or alkalis did not improve the growth. Since then I 

 have had the great majority of the bacteria described in 

 our atlas systematically studied as to their ability to grow 

 on the following nutrient media, by Dr. Winkler (Dissert. 

 Wiirzburg, 1896): 



1. On "neutral" agar, neutralized with normal soda 

 with the employment of phenolphthalein. 



2. On ' ' acid ' ' agar— i. e. , on neutral agar to which 

 was added 10 and 20 c.c. of normal sulphuric acid per 

 liter. 



3. On a sort of alkaline agar — i. e., on neutral agar to 

 which was added 10 c.c. of normal alkali solution per liter. 



The result, as indicated briefly in Table I (at end of 

 book), is that almost all bacteria grow well on these three 

 media. 



In every case the nutrient media neutralized by means 

 of phenolphthalein as an indicator may be implicitly 

 employed as universal nutrient media; moreover, the 

 virulence of those varieties tested by us (Bac. anthracis, 

 Bact. coli, Bact. of mouse septicemia and chicken cholera) 

 is well preserved thereon. 



This method has the advantage over other methods in 

 that it is easily carried out (compare Technical Appen- 

 dix), and that it represents a very exact point, namely 

 this, where all free acids and acid salts are changed into 

 neutral salts (mono-sodium phosphate into di-sodium 

 phosphate). 



Other recommendations — Timpe C. B. xiv, 845; Heim, 

 Lehrbuch, p. 73; Deelemann (A. G. A. xm, 374) — appear 

 to have no advantage. 



If an acid nutrient medium is to be employed, we think 

 it best to add 10-20 or 30 c.c. of normal acid to a medium 

 previously neutralized with phenolphthalein. According 

 to Winkler, the first degree of acidity is well borne by 

 almost all bacteria. According to the certainly not super- 



