MAN AND THE SEA, I 61 



impede circulation, leading to cramps. An allowance of an extra size should be 

 made if one plans to use a full rubber suit that covers the feet. 



The snorkel tube Cfg- ^5) is usually made of plastic, rubber, or metal. It 

 allows the swimmer to breathe surface air with the head under water and the 

 eyes out of the sun. One of its important features is that it permits the bodv 

 to float just a few inches below the surface at the point the body would normally 

 be in a dead man's float. Consequently, little energy is expended in keeping 

 afloat as compared to treading water without a snorkel. Thus, the swimmer 

 can swim great distances without tiring. The snorkel is a very simple device 

 to use. The valveless tube is used by the experienced swimmer and the ball-valve 

 type by beginners. A good technique for almost doubling your breath-holding 

 time under water is to take many quick, deep breaths before taking the last 

 one for the plunge; this rapid breathing before diving builds up oxvgen in the 

 blood. 



Safety under water, as in all other activities, works best when it is an attitude 

 rather than a set of rules, for trouble can come from unexpected directions. 

 Keep on the alert for the unexpected. 



The diver should carry at all times a very sharp, double-edged, pointed knife 

 for emergencies. He should also carry an emergency air pack (underwater 

 parachute), which, responding to a squeeze, will inflate, take the diver to the 

 surface, and keep him afloat. 



The Aqua-Lung or Scuba 



This self-contained underwater breathing apparatus gives the swimmer almost 

 all the freedom that a fish experiences. It allows the diver to go into deeper 

 water with litde effort, without the need to surface for air. It is useful to the 

 naturalist and especially useful to the photographer, for he can sit and wait 

 for opportunities. (Figure 131, the "kissing" grunts, was taken after one of 

 the authors remained still on the bottom at 35 feet for almost three quarters 

 of an hour.) The experience of using the aqua-lung in clear waters, abundant 

 with marine life, can be one of the most memorable in one's life. It can also 

 be the last. It is such a simple device to start using that the novice can easily 

 get himself into trouble. The authors recommend strongly that no one attempt 

 to use any self-contained underwater breathing apparatus without at least six 

 hours' training under competent instruction. Besides instruction on how to use 

 the lung, a portion of the six hours should be devoted to the part water pressure 

 plays in the aqua-lung's operation and to the eff^ect of pressure on the body. A 

 beginner would be wise to start with the snorkel, which will make him conscious 

 of his breathing, then move to the aqua-lung. 



BASIC SAFETY RULES 



1. Never dive alone; use the "buddy" system, and keep within sight of each 

 other. 



2. Plan in advance what is to be done in an emergency. Be sure all members 

 of a diving party know the technique for executing the back pressure-arm 

 lift method of artificial respiration. 



