Physiology of the Spermatozoa of Ferns. 563 
explain the results with sixty-five compounds by the help 
of a chemical theory. Unfortunately the attempt miscarried, 
‘ owing to a chemical misinterpretation as to the facts which 
give solutions their characteristic properties.’ In a footnote 
of a subsequent paper 1 Jennings has partially corrected his 
earlier criticism. The results of his work seem to leave little 
doubt that the chemotaxis of Paramecium follows certain 
laws to which the dissociation theory gives a clue. The 
theory has also been applied by Garrey 2 to the chemotaxis 
of Chilomonas. 
It must not be assumed that a chemotactic stimulus may 
be given only by ions. Just as some undissociated substances, 
such as alcohol, have a toxic action, so one finds undissociated 
substances giving a chemotactic stimulus. Thus, for instance, 
Pfeffer found that the 3 spermatozoa of Mosses are attracted 
by cane-sugar which is not dissociated, and his further work 
upon Bacteria has shown that a single species, e. g. 4 Bacterium 
termo , is attracted by a number of undissociated substances 
e. g. grape sugar, dextrin, milk sugar, mannit and asparagin 
in addition to such highly dissociated substances as sodium 
chloride, potassium nitrate and potassium sulphate. 
In testing the toxic action of solutions it appears to have 
been determined in some cases at least that even where the 
substance is highly dissociated the undissociated molecules 5 
have a toxic effect. We must therefore admit that when 
a highly dissociated salt (e. g. potassium nitrate as a 1 °/ o 
solution) attracts spermatozoa, the small percentage of undis¬ 
sociated molecules may have a chemotactic action. 
1 Study, V, On the movements and motor reflexes of the Flagellata and Ciliata. 
Amer. Jour, of Physiology, Jan., 1900. The footnote on p. 236 contains the 
above citation. 
2 Garrey, The effect of ions upon the aggregation of Flagellated Infusoria. Amer. 
Jour, of Physiology, Vol. Ill, p. 239, Jan., 190Q. 
Note. The papers of Jennings and Garrey came to my knowledge after this 
section of my paper was written. It has been altered only in so far as it was 
thought necessary to acknowledge their work. Garrey’s paper appeared six 
months after my work was brought to a conclusion. 
8 Pfeffer, loc. cit., Bd. i, p. 430. 4 Ibid., Bd. ii, pp. 603-605. 
5 Clark, loc. cit., pp. 282, 287, &c. 
