44 L. LEON CAMPBELL, JR. 



under anaerobic conditions. In Neurospora, Goddard demonstrated that the 

 spores could be reactivated at any time after anaerobic incubation by exposure 

 to air so that the process is entirely reversible. 



Harlyn Halvorson: Although Dr. Foster has pointed out that resistance 

 to heat probably does not play a major role of the natural selection of spores, 

 heat resistance remains as our only criterion of dormant spores. Since we 

 obviously require an operational definition of germination, until a clearer 

 basis of natural selection is available, it seems clear that we should employ 

 the loss of heat resistance as a measure of germination. Such a definition, 

 however, does not describe the activation of respiratory enzyme? in spores of 

 B. cereiis var. terminalis without the loss of heat resistance. In B. megaterium 

 on the other hand, respiratory activity parallels loss of heat resistance. How- 

 ever, other dormant enzymes of the B. cereus var. terminalis type may be 

 found. Therefore we should probably adopt the term "activation" to de- 

 cribe this stage prior to germination. 



MuRTY :• I wish to point out the difficulties of studying the effects of enzyme 

 inhibitors on germination if an increase in metabolic rate and ability for 

 outgrowth are included in the criteria of germination. As many of us al- 

 ready know, it is very difficult to inhibit germination as chacterized by de- 

 crease in optical density and ability to take up stain. Enzyme inhibitors like 

 arsenate, cyanide, etc., fail to stop these changes in optical density and stain- 

 ability of the spores. However, some of them do interfere with respiration 

 and outgrowth. It is further complicated by the fact that one cannot always 

 completely reverse the inhibition of respiration and outgrowth by washing. 

 Furthermore, the medium in which germination is studied seems to affect 

 the numbers of spores eventually outgrowing even when one washes the 

 spores and adds agents to reverse the action of the inhibitors originally 

 added. Thus there is a difference in the numbers of spores outgrowing, de- 

 pending upon whether they are allowed to germinate first in a simple, 

 chemically defined medium, often insufficient to support outgrowth, and then 

 transferred to a complete medium, or in a complete medium in the first in- 

 stance. I believe Dr. Powell also ran into a similar problem when studying 

 the effect of mercuric chloride on germination. So it appears that it may not 

 always be possible to use respiration and outgrowth as the criterion for 

 germination and especially so when studying the effects of inhibitors. 



