38 H. O. HALVORSON 



Further studies on this chemical have brought out a number 

 of interesting points in connection with the physiology of the 

 bacterial spore. Nearly all the dipicolinic acid is released into 

 the outside medium when the spores germinate. The release of 

 this acid correlates almost perfectly with the loss in heat resist- 

 ance, the loss in refractility, and the gain in stainability; and 

 this provides good circumstantial evidence that dipicolinic acid 

 plays an essential role in the unique heat-resistant properties of 

 spores. Studies which have been made on the activation of the 

 dormant enzymes through heat shock, germination, or mechani- 

 cal rupture also show a very good correlation between the 

 release of the dipicolinic acid and the activation of these 

 enzymes^^. This gives further circumstantial evidence for the 

 importance of dipicolinic acid in the protection of these enzymes 

 in the intact spore. The acid is also released from the spores 

 when they are killed by heat^^. This fact has been demonstrated 

 in a number of laboratories. The temperature that is required is 

 dependent upon the heat tolerance of the spores themselves. 

 Thus, the spores of thermophilic organisms must be heated to 

 a higher temperature to release the dipicolinic acid than those 

 of some less resistant aerobic organisms. In a recent announce- 

 ment by Foster^, he reports that dipicolinic acid can be released 

 from spores of B. megatherium at temperatures ranging from 

 70° to 100°. As the temperature is increased, less time is required. 



These numerous observations have led investigators in this 

 area of study to believe that spores are made heat resistant and 

 their enzymes protected by a complex collodial structure in- 

 volving a polymer formed from dipicolinic acid, calcium, and 

 special peptides. It would indeed be interesting to know more 

 about the nature of this complex. So far, it has remained 

 obscure because no means has yet been found to rupture the 

 spore and retain the complex. Any form of mechanical rupture 

 breaks up the complex and releases the dipicolinic acid in the 

 same way as germination does. The breaking of this complex 

 during germination may well be an enzymatic process and the 

 enzymes may be activated by mechanical rupture as well, so that 



