Modification of Genninal Constitution of Organisms 157 



4. In any experiments four parallel series must be 

 carried ; (a) a parent stock from which at the start is derived 

 the experimental stock, {b) the controlled stock reared 

 parallel to the parent stock but under controlled conditions, 

 (c) the experimental stock, which is a line culture sub- 

 jected to conditions of experiment and continued throughout 

 under the conditions of experiment, but from which is 

 taken at intervals, and {d) the test series, which are the 

 progeny of modified stock returned to conditions of the 

 control and parent, to test the constancy or reappearance 

 of induced modifications. 



5. All lines must be group cultures mated at random to 

 obviate in the fullest possible manner any traces of selective 

 effects; that is, to breed from pairs of selected extreme 

 individuals might easily lead to the selective accumulation 

 of germinal variations normal to the race, or the isolation 

 of hitherto unrecognized pure lines, and thus give rise to 

 false conclusions. 



If these conditions are complied with in any series of 

 experiments, the results will be an accurate answer to the 

 problem — no matter whether brief or long-continued action 

 be necessary to bring about the inheritance — because this 

 mav also be tested if the soma be modified at a time when the 

 germ is not sensitive, and if this be repeated generation after 

 generation the results obtained become more and more 

 certain in their value as evidence for one or the other side of 

 the controversy. 



Furthermore, experimental procedure of this kind will 

 at once give an answer to the question of the influence of the 

 soma as an environment upon the germ cell. That is, by 

 incident conditions it is easy to modify temporarily the 

 physiological state of the soma and gain further knowledge 



