Law of Proenvironi^ient 211 



strong, there would truly be a linking up and resultant response 

 as stated, but owing to the direction and strength of b it would 

 in appearance cancel a. Again under 2 the converse result 

 might be true. An explanation of 4 as being in reality a re- 

 sultant response might be given in several ways. Thus, if 

 the stimulant used so acted on some constituent molecules 

 of the organism as to cause the formation of a new chemical 

 compound, the presence of this might entirely alter the result- 

 ant response that might otherwise have been given. It would 

 scarcely be necessary now to cite other possible explanations. 



But, in reviewing all the observations made on Infusoria, 

 Jennings's conclusion (Jf2: 109) is of interest in our present 

 inquiry. For he says: "Why does the organism reject certain 

 conditions and retain others.^ We find that the animal rejects, 

 on the whole, such things as are injurious to it, and accepts 

 those that are beneficial. There are perhaps some exceptions 

 to this, but these are rare, and only noticeable because excep- 

 tional; in a general view the relation of rejection and accept- 

 ance to injury and benefit is evident. It results in keeping 

 the animal from entering temperatures that are above or below 

 those favorable for the life processes, in causing them to avoid 

 injurious chemicals of all sorts, in saving them from mechan- 

 ical injuries, and in keeping them in regions containing food 

 and oxygen. Clearly the animal rejects injurious things, and 

 accepts those that are beneficial." In other words, as we have 

 already expressed it, the organism plots a satisfied course. 



But all such movements are undoubtedly caused by one 

 or more external stimuli so acting on the protoplasm, or on a 

 localized part of it or of the cell contents, that these undergo 

 molecular changes. In some cases the general cell protoplasm 

 seems to be stimulated through the nucleus; since non-nucleate 

 cells are less often responsive, owing, as we would consider, 

 to the latter being traversed only by biotic, the former by 

 biotic-cognitic, lines of energy. In other cases perception 

 and proenvironal response are located wholly or most strongly 

 in a special center. • Thus Engelmann (38: 387) showed this 

 to be true for the anterior third of Euglena, and possibly even 



