THE VITAL CONDITIONS OF BACTERIA. 89 



1. Upon agar which, after the use of phenol- 

 phthalein, was neutralized with normal soda. 



2. On "acid" agar, i.e., neutral agar which has 

 been treated with 10 c.c. of normal sulphuric acid to 

 1 litre. 



3. On three varieties of alkaline agar, i.e., on neu- 

 tral agar which has received 10, 20, and 30 c.c. of 

 normal alkali to 1 litre. 



The results laid down in Table I. show, in brief, 

 that almost all bacteria thrive well upon three of 

 these nutrient media. 



At all events the medium made neutral by phenol- 

 phthalein may be recommended unreservedly as a 

 universal nutrient; the virulence of the varieties ex- 

 amined by us (anthrax, bacterium coli, mouse sep- 

 ticaemia, chicken cholera) was also well maintained 

 thereon. 



This reaction possesses the advantage that it is 

 easily prepared and represents a sharply defined 

 point, viz., that in which all the free acids and the 

 acid salts are converted into neutral salts (mono- 

 sodium phosphate into disodium phosphate) . 



If acid media are to be employed, it is best to start 

 with one which has been neutralized with phenol- 

 phthalein, to which 10, 20, or 30 c.c. of normal acid 

 per litre may be added. According to Winkler the 

 first degree of acidity is well tolerated by almost all 

 bacteria. According to Schliiter's statements (C. B., 

 XI., 589), which are confirmed by recent publications, 

 many tolerate a much higher degree of acidity ; even 

 as much at 100 c.c. of normal acid per litre, according 

 to experiments made in our laboratory. 



Apart from yeast and mould fungi, acid nutrient 



