3 30 THE CAUSATION OF DISEASE. 



are, doubtless, so subtle as to escape observation, but I doubt 

 not that often enough the difference could be easily accounted 

 for by observable differences in the E. 



And in a similar manner we can account for marked 

 differences between parents and offspring. Let us suppose a 

 healthy couple, of exceptionally good physique, to come up from 

 the country to live in the centre of London. We may safely 

 say of their children that all of them born and reared in 

 the lanes and alleys of the great city, will be very inferior, 

 physically, to their parents ; and we should, when comparing 

 the parents with the children, observe an apparent contradiction 

 to the law of heredity, for, according to it, a well-grown man 

 and woman should have well-grown sons and daughters. Cases 

 of this description are very common. I know of several myself, 

 and I have heard great surprise expressed that fine, strong 

 parents should have such puny and miserable -looking offspring. 

 Now, let the degenerate progeny of such healthy, well-grown 

 parents remove to healthy hygienic surroundings — such, e.g., 

 as obtain in the country — and the offspring of these will, if 

 reared in this healthy breeding ground, tend to grow up into 

 the physical likeness of their grand-parents — will revert, in fact. 

 Here we have the reverse picture of puny and ill-developed 

 parents rearing a well-grown and vigorous progeny, and again 

 it is argued that the principle of heredity is fickle and myste- 

 rious. Yet I maintain that it is nothing of the kind, and that 

 it only appears so because we fail to take into account the 

 many influences that may disguise it. I have purposely taken 

 extreme cases, where the difference in the E of parents and 

 offspring has been abrupt and marked, and in which, conse- 

 quently, the apparent contradiction to the law of heredity 

 can be easily explained, if we take care to compare the E 

 of parents and offspring ; but how many are the subtler 

 alterations of E which entirely escape our notice, and which 

 are, nevertheless, capable of profoundly affecting mental and 

 physical organization ? 



