164 Microbes and You 



and since the amount of oxygen per unit of air is reduced, nature 

 takes a simple way out by producing more oxygen-carrying cells. 

 Until these added cells are manufactured and put into operation, 

 however, deeper breathing can partially aid in relieving the lack 

 of the oxygen. Going back to sea level from higher elevations 

 requires a reverse adjustment phase, namely, a reduction in red 

 blood cells to the number more commonly found at sea level. The 

 length of the adjustment period varies with different people, and 

 during the transition period, it is not uncommon for individuals 

 to complain that they lack "pep." 



Deep sea divers cannot be returned too quickly to the surface 

 after being submerged at great depths, or the sudden release of 

 pressure on their bodies will cause the release of gas bubbles, 

 principally nitrogen, in the blood, causing the dreaded "bends" or 

 "caisson disease." Decompression chambers must be employed to 

 gradually return such divers to normal sea level pressures. Man 

 can endure remarkable changes in pressure if the changes are made 

 gradually. 



Getting back to bacteria, how much pressure can these microbes 

 endure without being killed? A great deal of conflicting informa- 

 tion exists on this point, but a direct pressure of 6,000 atmospheres 

 has been shown to kill non spore-bearing bacteria in 14 hours. 

 Some spores required twice this pressure for a similar time period to 

 be inactivated, but 20,000 atmospheres were required for still other 

 endospores to be killed. Anyone planning to stop the fermenta- 

 tion of grape juice by the application of pressure would be obliged 

 to exert 100,000 pounds pressure per square inch for 10 minutes to 

 accomplish this feat. Obviously there are more practical ways 

 of inhibitine microbial fermentation. There is evidence that 

 sudden osmotic changes are responsible for the death of organisms 

 subjected to extremes in pressure. A pressure of 12,000 atmos- 

 pheres may reduce the volume of water to 80% of normal, and 

 this same type of condensation of bacterial protein followed by 

 sudden release of the pressure would materially alter the colloidal 

 nature of the cells. Just as the sudden release of steam pressure 

 in an autoclave causes cotton-plugged tubes of media to "blow their 



