INTRODUCTION. 



Syphilis, as we all know, is communicated by the parent to his offspring, and 

 a frightful legacy it is. The mystery of original sin, the punishment " to the third 

 and fourth generation," are paralleled and vindicated by the observations of the 

 physiologist. On the other hand, certain diseases are not in the slightest degree 

 hereditary. A man may suffer for years from most distressing dyspepsia, and yet 

 -his children may exhibit no predisposition to stomach disturbance. Why certain 

 diseases should be transmitted and others not we do not at all know. We all 

 recognise the fact that certain conditions of the body are transmissible, that a son 

 may exhibit, not only the features, but the tone of voice, and even the very walk of 

 one of his parents. Hereditary transmission enters into the moral as well as into 

 the physical order of the world. It is common enough to hear it said of a man, 

 that he is a " regular chip of the old block," and we all believe more or less in family 

 likenesses, and that certain peculiarities of feature run in families. We say that a 

 boy has " his father's nose," or " his mother's eyes," as the case may be. 



Then, again, we know that features, form, frame, peculiarity of constitution, 

 susceptibility to certain agents, not to speak of character, mental and moral, the 

 passions and the intellect, are often derived from progenitors many steps upwards 

 in the ancestral tree. Individually we are combinations of many ancestors. The 

 actual traits of the parents may or may not be seen in their offspring, and it is more 

 common to find that one or two only are represented in each child. The remainder 

 are doubtless derived from some ancestor long forgotten, whose intellectual powers or 

 defects, infirmities or vigour of body, whose faults and follies, whose brilliant powers 

 or miserable failings, may be reflected in a remote descendant, as he himself has 

 derived them from some distant ancestor. We are accustomed to say that gout may 

 skip a generation, and why may not it skip four or five 1 Hereditary tendency is 

 probably of far more remote origin than is commonly supposed, and is a reflection of 

 the tendencies of untold numbers who have preceded us in the family tree. It is a 

 frightful thing thus to look back on the sins of our forefathers and to recognise the 

 transmitted punishment, but it is in accordance with other facts of moral origin and 

 highest dictation. 



It is sometimes asserted that when people live together, or are intimately asso- 

 ciated, they grow like each other, and we know that school-boys are apt to catch any 

 peculiarity of habit or expression of their tutor or schoolmaster. This is undoubtedly 

 the case, but it is a very different thing from heredity. Physical peculiarities 

 acquired accidentally are not transmitted. A man loses a leg, but his children are 

 born with their proper complement. For generations past it has been customary to 

 cut off the ears and tails of certain breeds of dogs, but it has not resulted in the 

 establishment of a race of animals unfurnished with these useful appendages. On 

 the other hand, when by a curious freak of nature a man is born with a supernumerary 

 finger or toe he may transmit this peculiarity to his children. It sometimes happens 

 that children of one sex exhibit an hereditary taint whilst those of the opposite sex 

 escape it. The boys " take after " the father and the girls after the mother, and a 

 tendency to disease may be more or less powerful as the child resembles one or other 

 parent. 



It would seem that certain conditions have a tendency to develop the hereditary 



