SHAKING 107 



lie applied the pressure very slowly to avoid any rise in temperature 

 due to the compression. That the effect is not due to heat is further 

 demonstrated by the fact that it is more easily obtained at C. 

 than at 20 C. The application of five thousand atmospheres pro- 

 duces stiffening of the white of egg; six thousand atmospheres 

 applied, for thirty minutes, produced an appearance of the white 

 resembling that of curdled milk; and seven thousand atmospheres' 

 pressure brought about complete gelatination. 



These facts seem to indicate that high pressure is fatal to many 

 bacteria. Experiments have shown this to be the case. B. anihracis, 

 B. pseudodiphtherice , M . pyogenes, var. aureus, and O'idium lactis 

 survived after being subjected to a pressure of 2000 atmospheres for 

 ninety-six hours. The pigment production and virulence of patho- 

 genic organisms were either diminished or completely lost after such 

 treatment. 



Successful attempts have been made to preserve fruit and vege- 

 tables by exposing them to high pressure. Apple juice subjected 

 to 4000 to 6000 atmospheres' pressure for thirty minutes did not 

 later develop gas. Peaches and pears exposed to this pressure did 

 not spoil for five years. Those vegetables on which are found resist- 

 ant spores could not be preserved by such pressures. It therefore 

 appears that pressure high enough for the coagulation of the proteins 

 is fatal to the less resistant bacteria. 



The power of resisting and actually functioning under high 

 pressure is especially necessary for the denitrifying bacteria which 

 live at the bottom of the ocean and return to the atmosphere the 

 thousands of tons of combined nitrogen which is carried each year 

 to the ocean from the soil and in the sewers. 



Shaking. It is well known that proteins may be coagulated by 

 shaking and that proteolytic enzymes undergo important modifica- 

 tions under the influence of shaking. An active solution of proteo- 

 lytic enzyme introduced into a reaction tube and agitated for two 

 minutes may lose as much as 75 per cent, of its activity. After five 

 minutes the disappearance is almost total. The effect of shaking 

 varies with the speed, temperature, and reaction of the medium in 

 which the ferment is placed. This phenomenon is known to be due 

 to a coagulation or absorption of the substance, and it is quite 

 possible that part of the influence exerted by shaking upon bacteria 

 is due. to this factor. It is known, however, that bacteria may be 

 broken into the finest particles by the rapid shaking of cultures 

 causing death at times by a disintegration of the cell body. 



