244 THE PRESEXT EVOLUTION OF MAN — PHYSICAL 



acquired traits in any true sense of the term. They 

 are, and for ever remain, foreign elements, just as a 

 rifle bullet that finds its way into the tissues is, and for 

 ever remains, a foreign element. The secondary infec- 

 tion of a germ or of an embryo through the parent, 

 therefore, no more imj^lies the transmission of an 

 acquired trait than the passage of a rifle bullet through 

 the body of the parent into the embryo implies it. 

 If, however, the effect produced by the passage of the 

 bullet on the parent's body were afterwards reproduced 

 in the unwounded developing body of the child, we 

 should then have a true example of the transmission of 

 an acquired trait ; so also, if the effects produced on the 

 tissues of the parent by the microbes and toxins of a 

 zymotic disease were reproduced in the non-infected 

 developing body of the child, we should have another 

 example of the transmission of an acquired trait. But 

 this certainly never happens : no non-tubercular child 

 of a parent who has phthisical cavities in his lungs ever 

 reproduces those cavities in the process of development ; 

 never are the pock-marks in the pitted skin of one who 

 has suffered from small-pox reproduced during develop- 

 ment by the non-infected cliild. 



Following a line of argument somewhat different 

 from that commonly used, and writing at a time when 

 the microbic origin of many diseases was unknown, Mr. 

 Herbert Spencer said — 



"But the clearest proofs that structural alterations 

 caused bv alteration of function are inherited, occurs 

 when the alterations are morbid. 'Certain modes of 

 liviucj enfjender crout,' and ffout is transmissible. It is 

 well known that in persons previously healthy con- 

 sumption may be produced by unfavourable conditions 

 of life — by bad and insufficient food ; by foul, damp, and 

 unvcntilated habitations ; and even by long-continued 

 anxiety. It is still more notorious that tlie consumptive 



