Let us suppose that an average healthy man during his lifetime acquires, by use, accident, or disease, some change in his right arm. There is no reason to suppose that the sexual cells, rather than any other cells in the body, will be affected. If, on the other hand, this local change in the arm affects the blood, depriving it of nutritive power, or casting into it obnoxious matter, then it is possible that all the cells of the body may be affected. We have many instances of such a thing, as when the blood and whole constitution are involved after maybe a primary local affection, and when, in consequence, the hair drops off, or marks and irregularities of the nails appear. In these cases the sexual cells may suffer from want of nourishment, or from what we may term a poison, and may produce less vigorous and perhaps diseased or malformed offspring, but they will show no tendency to develop in the offspring that primary local affection which caused ailment in the parent. But, as we shall see in the next chapter, the sexual cells in most cases get off scot-free, and the most dangerous acquired constitutional diseases leave no trace of their passage upon the reproductive elements. It is indeed difficult to point to a case, with the notable exception of syphilis, in which acquired constitutional blood disorders leave any trace in the organisation of the progeny, and we are indeed fortunate that this is so. There seems to be some evidence that we may stunt the growth of a plant or animal by insufficient or unsuitable food, and that all the cells of the body may thereby be reduced in size, the sexual cells among the rest, and that these reduced cells give rise to small progeny in the next generation. Here again the evidence in the case of animals seems rather doubtful, and rests on a few statements, such as that of De Quatrefages, that horses taken from Normandy to the hilly and less fertile country in Brittany become distinctly smaller in the course of three generations. In our own country large horses are found in the plains and small horses and ponies in the hilly districts of Wales and Scotland. But the obvious utility to man of small breeds in hilly districts, and of heavily-built horses on the plains, and the fact that horses have been bred for hundreds of years in view of their services to man, throws great doubt upon this particular evidence of De Quatrefages’, and we may well leave it out of account, unaccompanied as it is with evidence as to the total exclusion of the interbreeding of the Normandy with the Brittany variety.