x.] DISEASE. 183 



buted, and that the law of hereditary regression from 

 a deviation of three units on the part of cither 

 parent to an average of one unit in the child, may 

 be supposed to apply here, just as it did to Stature 

 and to the other subjects of the preceding chapters. 



Let the scale by which consumptivity is measured be 

 such that the Q of the general population = 1. Let 

 its M = N, when measured on the same scale ; the 

 value of N is and will remain unknown. Let N + C 

 be the number of units of consumptivity that just 

 amount to actual consumption. Our data tell us that 

 16 per cent, of the population have an amount of con- 

 sumptivity that exceeds N + C. On referring to 

 Table 8, we find the value of C that corresponds to the 

 Grade of (100 16), or of 84, to be 1-47. There- 

 fore whenever the consumptivity of a person exceeds 

 N + 1'47, he has actual consumption. 



Adding together the tabular values in Table 8 at all 

 the odd grades above 84, we shall find their average 

 value to be 2'23. We may therefore assume (see p. 160) 

 that a group of persons each of whom has a consumpt- 

 ivity of N -I- 2 '23 will approximately represent all the 

 grades above 84. The Co-Fraternity descended from 

 such a group will have an M whose value according 

 to the law of Regression ought to be [N + J (2 '23)] 

 or [N + 074 units.] 



Those members of the Co-Fraternity are consumptive 

 whose consumptivity exceeds N + 1'47 ; these are the 

 same as those whose deviation from [N + 074] which 

 is the M of the Co-Fraternity, exceeds + 073 unit. 



