All seven series give answers in the same sense, and we may conclude that we have definite experimental evidence that fatness increases the susceptibility to death from caisson disease. The regularity of the results in the guinea-pig experiments suggests that fatness is here the predominant influence in individual susceptibility. The difference in weight between the “survived” and ‘died” is not always in the same sense, and is in no case very large. The weight factor may therefore be relatively excluded in considering these results : indirectly it is of influence in that rats, like men, tend to become fatter as they grow older. Our results show pretty clearly that females are fatter than males, and, in the guinea-pig series, much more susceptible. Femality, like age, is not a quality which can per se have any influence on susceptibility. The increased susceptibility of females is probably simply due to their increased fatness, which tends to further increase during pregnancy. With regard to symptoms other than death our evidence is very meagre. Some symptoms, e.g. bends, may be presumed to be independent of fatness.