74 Life and Letters of Francis Galton 



disease. This seems to be confirmed by a strong inheritance of general physical 

 health independent of any special disease, which has been established since 

 Galton's inquiry. He purposely adopts in order to cover many popular expres- 

 sions the term "consumption." But beside actual consumption he graded in 

 three additional classes (for which he gives the rather vague descriptions 

 used), the context of the record also being considered*. These are (i) Highly 

 suspicious, (ii) Suspicious and (iii) Somewhat suspicious. He reckoned at the 

 rate of 4 of (i) to three actually consumptive, 4 of (ii) to two actually consump- 

 tive and 4 of (iii) to one such. Dividing a total of consumptives thus formed by 

 the total offspring he formed a ratio, which multiplied by 100 he termed the 

 " consumptivity " of the fraternity. For example, in a fraternity of which one 

 member was actually consumptive, two suspicious and four somewhat sus- 

 picious, Galton would reckon three consumptive members, and the taint, or 

 consumptivity, would be 43 °/ o . To his surprise he found on making frequency 

 distributions of consumptivity in fraternities, whether for one brother or one 

 parent consumptive, that low and high degrees of consumptivity were both 

 maxima, and moderate degrees gave a minimum or "anti-mode." Thus Galton, 

 as far as I am aware, reached the first U-shaped distribution of frequency. He 

 himself, notwithstanding his great belief in the normal curve, says it is not 

 possible to torture the figures so as to make them yield the single-humped 

 normal curve : 



" 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 marriages, which appears to be very small when statistically discussed, but 

 of whose occasional severity most persons have observed examples." (pp. 175-6.) 



Galton shows on pp. 177 and 179 by aid of very slender data, namely 

 1 4 fraternities with a "high " degree of consumption, which signified about 50 °/ c 

 deaths from lung trouble, and nine fraternities severely affected as to the heart, 

 that the parentages in the two cases were of a very different character. In 

 the latter case there was practically no distinction between the diseases from 

 which the father and mother died; in the former no more deaths than those 

 of two fathers could be associated with lung trouble, while some nine mothers 

 out of fourteen were consumptive. This led Galton to take the view that 

 consumption, while partly due to the inheritance of a tuberculous diathesis, 

 which may be transmitted equally by either parent, is also transmitted by 

 infection, and that in this respect the mother is by her closer contact far 

 more a source of infection than the father. Is this differential influence of 

 parents for tuberculosis confirmed by later investigations? I have taken the 

 unpublished results for some 400 phthisical patients in King Edward VII's 

 Sanatorium, and classified their parents into definitely phthisical and 

 "suspicious," where owing to mention of their ailments there was suspicion 



* See his pp. 172-3. Something of the same kind is still undertaken by tuberculosis officers 

 in grading the families of the admittedly tuberculous. 



