INFLUENCE OF A PREVIOUS IMPREGNATION. 267 



influence has been observed in fowls where the egg 

 is separated from the mother before the embryo is 

 developed that cannot have been produced by a con- 

 tamination of the blood of the mother by that of the 

 embryo. But another theory that has been advanced 

 to explain the manner in which this influence is trans- 

 mitted in mammals must be noticed. 



Prof. James Law, after mentioning some of the 

 theories that had been advanced to explain the phe- 

 nomena under discussion, says : " But a simpler and 

 more satisfactory explanation may be found. It is a 

 well-known pathological fact that adjacent cells tend 

 to ingraft their plastic or formative powers upon each 

 other. I prick my skin with a needle. Immediately 

 the injured cells and nuclei undergo a rapid increase 

 in size and numbers, but the effect does not end there ; 

 those adjacent take on a similar action, and the extent 

 of the resulting inflammation is only limited by that 

 of the injury and the susceptibility of the parts. 

 Again, in placing a slice of epidermis in the middle 

 of a raw sore we inoculate the cells of the adjoining 

 granulations, and empower them to develop epidermic 

 structure. How, then, can we avoid the conclusion 

 that the impregnated ovum impresses its own charac- 

 ters on the mass of the decidua, and, through this, on 

 the maternal placenta, and that this in turn impresses 

 its characters on the decidua and embryo of the next 

 succeeding generation ? " * 



This theory is certainly an ingenious one, but it 

 does not furnish a satisfactory explanation of all of 



1 " Reports and Papers of the American Public Health Association," 

 vol. ii., p. 263. 



