For subjects of all ages, one cubic centimeter of serum contains more than 1 Washington unit of streptococcal antitoxin in 64.6 per cent of 254 Canadian and in 93.5 per cent of 107 tropical sera. The mean potency of the tropical serum is significantly greater than that of the temperate zone. (A significant difference was judged to be one which could be detected 95 times out of 100.)

For subjects under 17 years of age, 44 per cent of 50 Canadian, and 93 per cent of 45 tropical sera contain more than 1 unit of antitoxin per cubic centimeter. The mean potencies differ significantly.

For adults, 69.6 per cent of 204 Canadian, and 93.5 per cent of 62 tropical sera contain more than 1 unit of antitoxin per cubic centimeter. The mean potencies are not significantly different.

Calculated on the basis of single tests, in each of which 6 rabbits were used, 25 cord samples contain more, and one less, antitoxin than the corresponding maternal serum, the remaining 66 pairs not differing significantly.

The cord serum can be shown to contain significantly more antitoxin than maternal serum if the mean difference for the 92 pairs of sera is considered as the basis of calculation.

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