1907.] Influence of Increased Barometric Pressure on Man. 15 
for one hour. Decompression was effected in four and a-half to seven seconds. 
In all, 85 rats have been used—54 small, 31 large; of the small rats, 14, 
or 25°9 per cent., died; of the large animals, 24, 77-4 per cent., died. 
Unfortunately, all the rats were not weighed, but we have records of the 
weight in 65 cases, and although this is not a great many from the statistician’s 
point of view, it is sufficient to make an analysis interesting. The following 
attempt has been made to measure the relationship between decompression 
effects and body weight. 
As we have no quantitative scale of decompression effects, the most 
satisfactory method to employ would seem to be that of fourfold division, 
obtaining the coefficient of correlation in the ordinary way(d5). We 
accordingly made the following table :-— 
Table IV. 
Weight in grammes. Recoveries. | Deaths. | Totals. 
Below 124 ........ui0 28 13 41 
ABOVE 124: 00.0. cusen 6 18 24 
: Totals ......... 34 | 31 | 65 | 
From this 7 was calculated to be 0°625 + 0°095. 
At first sight this would suggest a very close relationship between low 
weight and immunity from illness, but it is more than doubtful whether the 
fourfold method is applicable. 
For this process to be valid it is necessary that the distribution should be 
normal; thus, the modal severity of caisson illness should be neither 
among the very slight nor the very severe cases. As a matter of fact, 
human statistics show that “bends,” slight decompression effects, are vastly 
more frequent than severe or moderately severe paralysis, so that the 
severity distribution is, perhaps, skew, and 7, as found above, ceases to be a satis- 
factory measure of association. _We have, however, two more tests of 
statistical relationship, the correlation ratio (6) 
( __ Standard Deviation of Means of aor 
. Standard Deviation of the Character 
and the coefficient of mean square contingency (C,)(7). We can calculate 
m readily ; the mean weight of all the rats was 122°87 grammes, the standard 
deviation 67:08; the mean of survivors was 91°62 grammes, of victims 
15715, and » = 0°489. 
As a matter of fact this value differs from 7 by less than three times 
