MERCURY 



•Fig. 11-4 Smith Tube Test for the Presence of (or the Pro- 

 duction of) Enzymes in Yeast Cells Under Anaerobic Conditions. 

 The absence of nutrients precludes any considerable amount of growth. 

 A very large inoculum consisting of the growth from an entire agar 

 slant may be used in a single tube. The presence of constitutive 

 or adaptive enzymes can be determined by observing the rate of gas 

 production in the tube. Since there is no significant increase in 

 cell numbers selection is excluded. If gas production begins im- 

 mediately and continues without a change of rate, a constitutive 

 enzyme is present; if gas production begins after a lag period and 

 follows a sigmoid curve an adaptive enzyme is produced. 



In the tests shown in Fig. 11-2 and Fig. 11-3 it is impos- 

 sible to determine what causes the lag since growth must occur be- 

 fore gas is produced. An opportunity for the selection of a 

 mutant from a predominantly nonfermenter population may occur in 

 tests involving growth, but is excluded in the Smith tube when 

 mercury is used. In this test the anaerobic evolution of CO2 can 

 be calculated for a stationary population just as it can in the 

 Warburg apparatus. 



The van Iterson-Kluyver apparatus is another device which ac- 

 complishes the same end as the Smith tube with mercury. It is, 

 however, more complicated since it contains several glasscocks and 

 in our experience seems less desirable because of the loss of mer- 

 cury on table tops and floor. These authors use a sugar solution 

 containing nutrient, but we have found that the evolution of gas 

 occurs quite readily in the Smith tube over mercury with only 

 phosphate and sugar, if 50 mgm (dry weight) of yeast is used. 



'The more elaborate Warburg apparatus presents (1) a measure 

 of the rate of evolution of CO2 m the presence of N2 or U) in 

 air and (3) the rate of consumption of oxygen. When the dryweight 

 of yeast used is obtained the rate can be expressed in terms ol 

 mm3 of ^as per hour per mgm of dryweight. 



11-11 



