22-5 THE YEAST CELL 



and 07 . Each tube was inoculated in a uniform manner with a loop. 

 Three hundred colonies grew from each loopful of inoculum used, 

 but since the haploid cells were typically aggregated, the total num- 

 ber of cells in each inoculation was probably about 1500. 



Fig. 22-1 shows the results with a diploid culture of S. cerevisiae 

 (No. 1); the turbidity is plotted against time in hours. The graphs 

 are made by plotting the average of the turbidity produced in the du- 

 plicate tubes, except in a few cases in which the tubes were so wide- 

 ly different that averaging did not seem to be a permissible practice. 

 Usually the readings differed by only a few units and averaging was 

 obviously acceptable. After 45 hours, growth is practically com- 

 pleted in the media containing 50 and 1007 of pantothenate, but it is 

 fully 75 hours before appreciable growth is recorded in the tube with- 

 out added pantothenate. This culture had previously been character- 

 ized as a synthesizer of pantothenate. These data show that diagnosis 

 depends largely on the time at which readings are taken. Comparison 

 of the 1007 and 07 tubes at the end of 45 hours would have resulted 

 in characterizing this particular organism as a "non-s5mtliesizer'' of 

 pantothenate. The relationship between the amount of added panto- 

 thenate and the time at which growth begins is quite clear since the 

 curves are all closely parallel during early and logarithmic growth 

 and overlapping of the curves only occurs after the logarithmic phase 

 of growth has been completed. There is a sharp difference between 

 the time at which growth begins in the tubes containing 0.5 and 17 of 

 pantothenate per liter as well as between growth in tubes containing 

 1 and 27 of pantothenate per liter. 



The culture of S. cerevisiae, whose reactions are recorded in 

 Fig. 22-1, was induced to sporulate, and similar tests with the four 

 haplophase cultures are shown in Figs. 22-2 and 22-3. Cultures No. 

 3 and No. 4 are remarkably similar in behavior. According to pre- 

 vious techniques these would have been classified as "non-sjmthesizers* 

 because growth in the absence of pantothenate did not begin until after 

 250 hours. The particularly interesting feature of the behavior of these 

 cultures is the close relation between the lerigth of the delay before 

 growth begins and concentration of pantothenate in the medium. 



In culture No. 5 (Fig. 22-2) the different concentrations of panto- 

 thenate also bear a direct relation to the delay before growth begins. 

 A similar picture exists for culture No. 6, except that in the concen- 

 trations of 17 and 07 per liter the duplicate tubes differed so markedly 

 from each other that it was not permissible to average the results. 

 This is one of the few cases in which growth in l7 per liter in one of 

 the duplicate tubes occurred later than growth in the tube containing 

 0.57 per liter. 



The behavior in culture No. 5 (Fig. 22-2) is an almost ideal ex- 

 ample of the phenomenon. Growth in media containing lOOr and 507 

 per liter takes place at a very rapid rate. In the medium containing 



