182 VARIATION OF SPECIES 



ture of sporulation. Inversely the minimum temperature of budding 

 is always a little lower than that for sporulation. What happens, 

 then, if one allows the yeasts to remain for a period between these 

 two temperatures? Such is the question that Hansen tried to solve. 

 He obtained a complete loss of the ability to sporulate by cultivating 

 a number of the yeasts for generations in beer wort at a temperature 

 higher than the maximum for sporulation. He could not obtain the 

 same results by placing the yeast at a temperature lower than the 

 minimum for sporulation. The transformation is accomplished slowly 

 and by successive culturing; the number of sporogenic cells gradually 

 diminish until they totally disappear. Thus may be obtained as- 

 porogenic varieties which may be maintained indefinitely. Hansen 

 has been able to keep them for sixteen years without taking up the 

 sporogenic property again. The types of yeasts thus secured may 

 be regarded as constant. These varieties offer new characteristics 

 which give evidence of profound modifications in the structure of their 

 protoplasm. The power of budding often increases and the colonies 

 present a different appearance than yeasts. On the other hand, all 

 of the varieties thus obtained, with certain rare exceptions, seldom 

 produce a scum. Thus the loss of power to form spores is a charac- 

 teristic definitely acquired by this variety when cultivated for a 

 certain time on beer wort at a maximum temperature for the form- 

 ation of endospores. 



This transformation of a species which is sporogenic into an as- 

 porogenic type is a most typical example of an acquired charac- 

 teristic which may approach the attenuation of a virus, as shown by 

 Pasteur. How Pasteur attenuated the Bacillus anthracis by grow- 

 ing it at a temperature of 42-43 C. is well known. Not only the 

 toxic properties of the bacillus disappeared but also its sporogenic 

 functions. Here we have the creation of a new type characterized 

 by the loss of virulence and ability to form spores. 1 



How does this loss of ability to sporulate in yeasts operate? Is 

 it a transformation or a selection? Hansen does not regard it as a 

 selection because many of the cultures of yeasts which he used to 

 produce this spprogenic type, especially the yeast Johannisberg II, 

 contains only sporogenic cells. Numerous observations have convinced 

 him that an asporogenic cell exists in this culture. It must be a typi- 

 cal transformation. 



Hansen has shown that by varying the composition of the medium 



1 Hansen has approached this transformation of a sporogenic into an asporo- 

 genic yeast by certain variations which have been observed in the higher plants. 

 In America the banana reproduces asexually while in mid-Asia it reproduces 

 sexually. 



