CHEMOTAXIS 25 
chemicals is a purposive trait, although many forms do not 
react away from solutions which are decidedly injurious. 
According to Massart Polytoma uvella may not be repelled 
even by the strongest chemicals. Other organisms while 
perfectly able to swim away, do not seem to be prepared for 
meeting such a situation as the presence of injurious chem- 
icals by any appropriate response. If specimens of Loxo- 
phyllum meleagris and Parameecium are placed together 
under a cover-glass and a small drop of acid applied to one 
edge the Parameecia will avoid the acid, but the Loxophylla 
move about helplessly, many of them swimming directly 
into the strong acid, others which may be overtaken by the 
acid showing no more tendency to swim away from it than 
toward it. The result is that nearly all of the Paramecia 
in the region of the diffusing acid escape, while nearly all 
of the Loxophylla perish. 
The general tendency of Parameecium to collect in all kinds 
of weak acid and to react negatively to alkalies is prob- 
ably of little service to the organism. Bacteria show a posi- 
tive reaction to various substances which they never encoun- 
ter under normal conditions and whose presence can scarcely 
be of any benefit to them. On the other hand, the positive 
reactions of several species to oxygen, as well as the negative 
reactions of certain anaerobic species, are doubtless beneficial 
modes of response. It is not improbable that in many 
cases the response to substances that are not beneficial is 
the incidental result of the organization which causes posi- 
tive responses to substances that are beneficial. For 
instance, it may be advantageous to Paramcecium to be con- 
stituted so as to react positively to weak solutions of carbon 
dioxide, and its positive response to other weak acids may 
depend upon the same peculiarity. While much of the 
chemotactic behavior of lower organisms may be indifferent 
