Carbon Assimilation and Respiration 11 



Treatment 



Regular medium — Con- 

 trol 



Regular medium — Inocu- 

 lated 



1 per cent. Dextrose — 

 Control 



1 per cent. Dextrose — 

 Inoculated 



0.1 per cent. XaHC0 3 — 

 Control 



0.1 per cent. XaHC0 3 — 

 Inoculated 



0.1 per cent. NaHC0 2 + 

 H 3 P0 4 — Control 



0.1 per cent. NaH00 2 + 

 H 3 P0 4 — Inoculated .... 



Atmosphere 



Ordinary 



C0 2 free 



Final 



P H 



Titre 





Titre 



4.2 



2.20 



4.2 



2.20 



1.2 



12.15 



3.8 



2.25 



3.0 



2.20 



3.0 



2.2 



1.2- 



13.15 



2.8 



2.33 



6.6 



1.3 



6.6 



1.3 



5.4 



2.0 



6.0 



1.75 



6.2 



2.2 



6.2 



2.2 



1.5 



9.3 



5.3 



2.5 



No growth took place in the carbon-dioxide free atmosphere 

 both in the absence and presence of dextrose. The slight in- 

 crease in acidity of the inoculated culture is due to the inoculum 

 introduced (3 drops of culture in 100 c.c. of medium). How- 

 ever, in the presence of the bicarbonate, a slight amount of 

 growth took place even in the C0 2 -free atmosphere. The rela- 

 tively small growth made in the presence of the bicarbonate is 

 due to the change in reaction of the medium, the organism hav- 

 ing its optimum at Ph 2.0 to 5.0 (1.0-5.6). 



For studying the respiration of bacteria, the methods of 

 Osterhout 2 and Meyerhof 3 are available. The former is not 

 very suitable for the study of the autotrophic bacteria, since the 

 organisms consume carbon dioxide and produce acids which 

 rapidly change the reaction of the medium. The method used 

 by Meyerhof was found more suitable. By this method we 

 measure the amount of change in the concentration of substratum 

 produced in a definite period of time, as a result of the energy 

 utilization by the organism. We can thus differentiate between 

 the growth and respiration processes. 



Sulf. thiooxidans was grown in the above medium till the 

 maximum rate of growth was attained, as determined from the 



2 Osterhout, W. J. V., J. Gen. Physiol, 1918, i, 171. 



3 Meyerhof, O., Arch. Ges. Physiol., 1916, clxiv, 353; clxv, 229; clxvi, 240. 



