58 THE CAUSATION OF DISEASE. 



tissue-structure, and therefore similar disease tendencies, or 

 actual disease, at corresponding ages. The S varying with the 

 age, the effect of E upon it will likewise vary at different 

 periods of life, and hence the tendency to disease will vary too. 

 In some cases there seems to be a tendency towards inheritance, 

 not at the corresponding age, but at an earlier age, in the off- 

 spring than in the parent. This often happens, for instance, in 

 gout ; and Darwin points out that, when the rule is departed 

 from, the inherited peculiarity appears earlier rather than 

 later, for he says, "the exceptions in the other direction are 

 very rare." The facts of embryology certainly bear out this 

 observation.* 



We may also speak of an heredity at corresponding seasons ; 

 for, as we have seen, there is an annual organic cycle 

 corresponding to the annual cycle in the E. We may in- 

 stance the horns of the stag, which appear at certain seasons, 

 or indeed, the skin appendages of most animals, such as the 

 feathers of birds, the fur or hair of animals, the scales of fish, 

 which undergo periodic changes at different seasons. These 

 changes are, as we have seen, ultimately dependent upon the 

 seasons ; but they come to be very largely inherited, so that, 

 although the alteration of the seasons is necessary to show them 

 in their most typical form, they would tend to appear independ- 

 ently of the seasons, through the force of inheritance pure and 

 simple. It is probable that the same kind of skin changes occur 

 in man. This would account, in some measure, for the espeeial 

 prevalence of certain skin diseases at particular periods of the 



* When an inherited character appears earlier in the offspring than in the 

 parents, we have an example of "precocity." One of the most interesting 

 instances of precocity is the occurrence of puberty before the wonted time. 

 There is a fair number of such cases on record. I have now under observa- 

 tion a boy, who, at the age of two years, attained full sexual maturity. His 

 testicles and penis are fully developed ; there is abundance of hair on the 

 pubes, his voice is gruff, and his muscles stand out boldly like those of a well- 

 grown man. The sexual instinct is strong and troublesome. All will agree 

 that this case is abnormal and unfortunate ; but when a similar precocity is 

 exhibited in other directions, the parents are often apt to regard the individual 

 as a prodigy, as a wonder of whom great things must be expected. I refer 

 especially to cases of premature cerebral development. No doubt, in certain 

 cases, this promise of youth is an earnest of a great future, but, as a general 

 rule, precocity is abnormal— a thing altogether to be regretted, whether of the 

 brain or of the reproductive system. 



