INTRODUCTION 17 



mary to call tlie fundamental generalizations of the science 

 the ''laws" of that science, so we may call the foregoing 

 generalizations, the six laws of heredity known to us at 

 present. Despite the fact that the use of this word '4aw" 

 has been much abused in popular biological writing we 

 need not apologize for using it here, because the postu- 

 lates in question have been established by the same scien- 

 tific procedure that chemists and physicists make use of, 

 viz., by deductions from quantitative data. Excepting for 

 the sixth law they can be stated independently of the chro- 

 mosomal mechanism, but on the other hand they are also 

 the necessary outcome of that mechanism. 



The theory of the constitution of the germ-plasm, 

 to which Mendel's discoveries led him, not only failed to 

 receive any recognition for fifty years, but the principle 

 of particulate inheritance to which it appeals has met 

 with a curious reception even in our own time, leading 

 a recent writer to state that particulate theories in general 

 "do not help us in any way to solve any of the funda- 

 mental problems of biology, ' ' and another writer to affirm 

 that if the chromatin of the sperm is "pictured" as com- 

 posed of individual units that represent "some specific 

 unit-characters of the adult, ' ' then we should expect it to 

 be extremely complex, "more complex indeed than any 

 chromatin in the body, since it is supposed to represent 

 them all," but "as a matter of fact chemical examination 

 shows the chromatin in the fish sperm to be the simplest 

 found anywhere. ' ' Were our knowledge of the chemistry 

 of the "chromatin" as advanced as these very positive 

 statements might lead one to suppose, the objection raised 

 might appear to be serious, but there is no evidence in 

 favor of the statement that the sperm-chromatin should be 

 expected to be more complex than the same chromatin 

 in the cells of the embryo or adult. And even were it 

 different in the germ-tract and soma the criticism would 

 miss its mark, because heredity deals with the constitution 

 of the chromatin of the germ-tract and not with that of 



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