308 MICRO-ORGANISMS AND FERMENTATION. 



One object of Hansen's work was to determine to what 

 extent the formation of spores was influenced by different 

 temperatures, with a view of ascertaining whether the various 

 species behave alike, or whether it might not be possible in 

 this way to discover characteristics. It was necessary to 

 determine : First, the limits of temperature i.e., the highest 

 and lowest temperatures at which spores can be formed ; 

 secondly, the optimum temperature i.e., the temperature at 

 wMch spores appear most rapidly ; and, thirdly, the relation 

 between the intermediate temperatures. 



To determine the time required, the moment was registered 

 at which the cells showed distinct indications of spores (com- 

 pare Figs. 52 and 58). It is not possible to make use of ripe 

 spores in these determinations, since no criterion exists for 

 complete ripeness. 



Fig. 57. Germination of spores of Saccharvmyces anomalug (after Hansen). 



The results obtained by Hansen are as follows : 

 The formation of spores takes place slowly at low tem- 

 peratures, more rapidly as the temperature rises, until a point 

 is passed at which their development is retarded and finally 

 ceases. 



The lowest limit of temperature for the six species first 

 investigated was found to be 0-5-3 C., and the highest limit 

 37-5 C. Hansen also determined the intermediate tempera- 

 ture and time relations for the six species, and found that 

 when these two values are graphically represented, with the 

 degrees of temperature as abscissae, and the time intervals as 

 ordinates, the curves are almost identical for the six species. 



