TITRATION AND ADJUSTMENT OF CULTURE MEDIA 227 



The peptone solutions were then divided into two sets (as 

 with the meat infusions), one corrected and the other uncor- 

 rected. These were given successive treatments in the auto- 

 clave and titrated at the same intervals. As with the meat 

 infusions there was a steady increase in acidity though not in so 

 marked a degree. Three uncorrected portions of peptone solu- 

 tions (Fairchild's, Eimer and Amend, Squibbs) were also run 

 an additional six hours, making fourteen hours in all in the 

 autoclave. As with the meat infusions the hmit of hydrolysis 

 was not reached. 



In the corrected portions the total amount of acidity, developed 

 by heating after successive additions of normal soda, again 

 paralleled closely the rise in acidity of the corresponding un- 

 corrected portions. 



From the above it is apparent that the introduction of a 

 peptone into a medium will affect the reaction to some extent. 



INDICATORS 



The shade of phenolphthalein suitable for a correct end point 

 varies greatly in the opinion of different authors. 



Miur and Ritchie (1913) give "the first trace of pink." 



Hiss and Zinsser (1914) — "faint but clear and distinct pink." 



Stitt (1913) — "a delicate pink (hot titration) a purplish violet 



color (cold titration)." 



Jordan (1914) — "Faint but distinct pink color." 



Park and Williams (1914) — "Faint, bub distinct pink which remains 



on re-heating." 



Heinemann (1911) — "Faint but decided and stable pink." 



Abel (1912)— "Brilliant red." (Translation.) 



Abbott (1915)— "Pink color." 



MacNeal (1914) — "Faint but distinct and permanent pink." 



Swithinbank and Newman (1903)— "Clear bright pink color." 



Mallory and Wright (1915) — "Bright pink color" not "the pinkish 



darkening of the fluid which preceeds it." 



Eyre (1915) uses a "pinkish tinge" or "a faint rose-pink which 



cooled to 30° or 20°C., becomes more distinct and decidedly deeper 



and brighter" resembling a "deep magenta color." 



