the lung contents of six workers who had been occupationally exposed to chrysotile asbestos were examined . 
 five were lung cancer cases from quebec , canada . 
 the sixth , an american worker who had developed pleural mesothelioma , was particularly interesting , with the lung content strikingly distinct from the canadian cases ; chrysotile , the predominant fiber in his lung , was present at a concentration 300 times that of the average total fiber content in the canadian cases . 
 the fiber length distribution of the chrysotile recovered from the u.s . 
 mesothelioma case was indistinguishable from that of chrysotile specimens known to produce mesotheliomas in rats . 
 it was also found that the characteristics of the calcium - magnesium - iron silicate fibers present in all six cases were not readily comparable to tremolite asbestos specimens known to induce mesotheliomas in animals.imagesfigure 1 . 
 afigure 1 . 
 bfigure 1 . 
 cfigure 1 . 
 dfigure 2 . 
 afigure 2 . 
 bfigure 2 . 
 cfigure 2 . 
 d