140 GENERAL PHYSIOLOGY 



quired to kill these is spoken of as the absolute thermal death 

 point. There have been two methods widely used for the 

 determination of the thermal death point : one devised by 

 Sternberg, who uses a glass bulb, and the other described by the 

 Committee on Standard Procedures appointed by the Ameri- 

 can Public Health Association. In both of these methods 

 only the absolute thermal death point is determined, and each 

 method has certain advantages and certain disadvantages. 

 A capillary bent tube method, which was devised in the labora- 

 tory of one of us, offers certain advantages over both of the 

 other methods. Death from heat is undoubtedly due to the 

 coagulation of the protoplasm, and the different protoplasms 

 have different points of coagulation. One difference which may 

 account for these variations is the different amount of mois- 

 ture present. This would tend to explain, especially, the 

 high thermal death point of spores compared with the vege- 

 tative cell. 



Egg albumin + 50 per cent water coagulates at 56 C. 

 Egg albumin + 25 per cent water coagulates at 74-8o C. 

 Egg albumin + 18 per cent water coagulates at 8o~9o C. 

 Egg albumin + 6 per cent water coagulates at i45C. 

 Egg albumin dry coagulates at i6o-i7o C. 



The Action of Chemicals on Bacteria. Reference has 

 already been made to the chemical reaction of the media, 

 and the influence which it has upon the development of the 

 bacteria. It was noted that the bacteria preferred a neutral 

 or slightly alkaline medium rather than an acid one, although 

 they will tolerate one that is slightly acid. 



