250 



JOHN T. MYEKS 



Cystin plus tartaric acid behaved in a similar manner. 



Finally a 0.5 per cent, solution of cystin was prepared by 

 adding just enough sodium carbonate to keep the cystin in 

 solution. The medium was sterilized by filtration because heat 

 caused hydrogen sulphide formation. It was placed in sterile 

 tubes and tested for sterility. Tubes were inoculated with the 

 series of organisms used with the sodium sulphate and taurin 

 mediums. After a week's incubation no growth appeared. 



Another series of tubes were inoculated with the same bacteria 

 used previously. A bit of sterile litmus paper was added to each 

 tube and sterile 5 per cent, hydrochloric acid added till the litmus 

 was faintly red. The cystin was precipitated as the neutral 



TABLE 7 

 Formation of hydrogen sulphide from a solution of cystin, in millimeters of lead 



acetate paper blackened 



ORGANISM 



B. paratyphosus B 



B. typhosus 



B. cloacae 



B. proteus 



B. fluorescens liquifaciens 



24 hours 48 hours 72 hours 



7 

 

 

 4 

 15 



7 DATS 



7 











25 



25 



point was approached but this was ignored. After three days 

 incubation the litmus turned blue and sterile acid was again 

 added till it turned faintly red. Growth appeared in all the 

 tubes and hydrogen sulphide was formed in some of them. 

 Table 7 gives the results. 



This experiment was repeated except that the cystin was 

 dissolved in the smallest possible amount of tenth normal hydro- 

 chloric acid and tenth normal sodium carbonate was added till 

 a precipitate formed and the medium was only slightly acid, the 

 exact reverse of the preceding method. The results were the 

 same. 



Cystin could doubtless have been sterilized by dissolving it in 

 an organic solvent, evaporating this off and adding sterile dis- 

 tilled water but this was not tried. 



