38 CHEMICAL AGENTS AND PROTOPLASM [Cn. I 



organs arise, so that it seems probable that it occurs in the 

 mouth of the archigonium, and that by its presence sperma- 

 tozoids are attracted towards the egg cell. 



STANGE ('90, p. 155) has experimented much more fully 

 with the action of organic acids upon zoospores of Saprolegnia 

 and upon myxamcebse. To the former, acetic acid (0.01%) and 

 tartaric acid (0.0125%) act attractively. Upon the latter, still 

 other acids were tried; butyric, lactic, and valeric acids cause 

 response in concentrations between 0.2% and 4% ; malic acid, 

 between 0.5% and 4%. Other attracting acids are : propionic, 

 citric, tartaric, and tannic. Acetic acid repels the amoebae of 

 JEthalium, its repellent action being about equal to the attrac- 

 tive action of an equal amount of butyric acid. 



Nitrogenous Compounds. Urea, asparagin, kreatin, taurin, 

 hypozanthin, carnin, and peptone have been found by PFEFFER 

 ('88) to exert an attractive influence, especially in the case of 

 the reagents italicized. 



Benzol Derivatives. PFEFFER found that sodium salicylicate 

 and (commercial) sulphate of morphine are clearly attractive to 

 Bacterium termo in 1% solutions. 



From the foregoing list of organic compounds whose effect 

 upon Protista has been tested by PFEFFER and STANGE, it 

 appears that except alcohol and sometimes acetic acid, none 

 acts repulsively, and that glycerine alone is neutral to all proto- 

 plasm. It is further true that we do not find here any strict 

 relation between the chemotactic action of a substance and its 

 advantage to the organism. Substances which have a nutri- 

 tive value for the organism, such as glycerine has for bacteria, 

 may be wholly neutral, while solutions which act fatally, like 

 1% sodic salicylicate and 1% morphine, attract. In the same 

 way, many of the organic salts which act attractively cannot 

 be considered as of importance to the organism. On the other 

 hand, as already pointed out, the attraction of most Protista to 

 oxygen, of Saprolegnia zoospores to phosphates, as well as the 

 cases of attraction of bacteria (PFEFFER, '88, p. 605) and of fly 

 larvae (LoEB, '90, p. 79) to meat extract, and of Myxomycetes 

 to bark extract (STAHL, '84 ; STANGE, '90), is advantageous. 

 Chemotaxis is, therefore, in some cases, a response to the 

 stimulus afforded by substances which can be employed by 



