6 PREFACE 



problem, but have dealt almost entirely with 

 amoebae, our object being to determine if possible 

 the way in which auxetics and kinetics are capable 

 of exciting reproduction in these cells, and how 

 they are produced in nature so as to have this 

 action. The amoeba was selected for this purpose 

 as a type of individual cell which can readily 

 be cultivated and in which the common vital 

 phenomena of movement, nutrition, and par- 

 ticularly reproduction can be watched with com- 

 parative ease, and the influence of chemical agents 

 on these processes can be tested with a certain 

 amount of precision. But a more important point 

 for our purpose is the fact that amoebae depend for 

 their existence under natural conditions on the 

 growth of accompanying bacteria, and, as auxetics 

 and kinetics are prominent among the products of 

 bacterial activity, the effects of these substances can 

 be studied as they are actually being produced. 

 As side issues in the investigation, we have 

 examined the influence of environment on morph- 

 ology and life-history from a chemical point of 

 view, as the factors concerned in the production of 

 cell variation are still so little understood. As a 

 subject for experimentation, however, when com- 

 pared with tissue and other cells, amoebae have one 

 disadvantage in that they periodically exhibit the 

 remarkable phenomena of encystment and excysta- 

 tion. We had previously been able to induce 

 divisions in the resting spores of Polytoma (P. 

 granulosd) by various combinations of auxetics and 



