176 CHALLENGER 



travelled to see the Sheikh and over coffee the offending holes 

 were pointed out. It was with some reluctance, Bill thought, that 

 the Sheikh exchanged the carpet for the other, which by day 

 appeared infinitely superior in that it was intact. 



Throughout Challenger^ s three surveying seasons in the Persian 

 Gulf there had nearly always been one or two men in the sick 

 bay suffering from what was known onboard as coral ulcers. There 

 was much walking upon the coral reefs to be done, both while 

 erecting the triangulation marks and when wading along the 

 reef's edge to delineate it as one would the coastline. On such 

 occasions those who had been walking in the shallows might com- 

 plain within 24 hours of severe pain as they stood. Soon a deep 

 ulcer would form, usually in the vicinity of or a little above 

 the ankle. Such persons might for weeks be incapacitated and be 

 in considerable pain on setting foot on deck. Surgeon Lieutenant 

 Preston made a study of this ailment and wrote up his findings 

 for the British Medical Journal. He found little literature upon the 

 subject although he found the condition well known among the 

 local fishermen and those who had been employed in pearl diving 

 in the Gulf. Wyville Thomson, the scientific leader of the 

 Challenger Expedition of 1872-76, had referred briefly to the 

 condition, which had been contracted by sailors from that vessel 

 walking upon the reefs without wearing stout boots. 



The corals which form these extensive, almost vertically sided 

 reefs are attached creatures living in great colonies, built up of 

 calcium extracted from sea water and feeding upon small marine 

 organisms. Preston found that in order to secure its food each 

 coral polyp possesses specially adapted outer cells known as 

 nematocysts ; these stinging organs contain a coiled thread ending 

 in a dart-like silica head which is filled with powerfully toxic 

 fluid. The whole apparatus is developed in a cell called a cnido- 

 blast which is at one point elongated into a so-called cnidocil or 

 trigger-hair. When this is broken by a passing organism or body 

 the cnidoblast ejects the dart with considerable force into the 

 victim, which is completely paralysed by the rapidly spreading 

 poison. 



These darts are probably unable to penetrate the human skin, 

 but when this has been lacerated by contact wdth the sharp 



