x.] DISEASE. 175 



They struck me as so remarkable, in the way shortly 

 to be explained, that I proceeded to verify them by as 

 different a set of data as my Records could afford. I 

 took every fraternity in which at least one member 

 was consumptive, and treated them in a way that would 

 answer the following question. " One member of a 

 fraternity, whose number is unknown, is consumptive ; 

 what is the chance that a named but otherwise un- 

 known brother of that man will be consumptive also ? " 

 The fraternity that was taken above as an example, 

 would be now reckoned as one of nine members, of 

 whom one was actually consumptive. There were 84 

 fraternities available for the present purpose, and the 

 results are given in the line B of the table. The data 

 in A and B somewhat overlap, but for the most part 

 they differ. 



They concur in telling the same tale, namely, that it 

 is totally impossible to torture the figures so as to make 

 them yield the single-humped " Curve of Frequency " 

 (Fig. 3 p. 38). They make a distinctly double-humped 

 curve, whose outline is no more like the normal curve 

 than the back of a Bactrian camel is to that of an 

 Arabian camel. Consumptive taints reckoned in this 

 way are certainly not " normally " distributed. They 

 depend mainly on one or other of two groups of causes, 

 one of which tends to cause complete immunity and 

 the other to cause severe disease, and these two groups 

 do not blend freely together. Consumption tends to 

 be transmitted strongly or not at all, and in this respect 

 it resembles the baleful influence ascribed to cousin 



