Physiology of the Spermatozoa of Ferns . 545 
the pressure of the air the tubes become partly filled with 
the liquid. A tube is then removed from the solution, washed 
by dipping in water and placed under the coverglass of a 
preparation in which spermatozoa or Bacteria, &c., are 
swimming. If the solution attracts the organisms they 
collect in the tube, if it repels them they refuse to enter, 
while if it does not exert a directive stimulus they move in 
and out of the tube with apparent indifference. This method 
has been used by Massart, Voegler, Miyoshi and myself. 
Pfeffer’s researches were made upon spermatozoa (particu¬ 
larly those of Ferns), swarmspores, gametes, Bacteria, Flagel- 
lata, Volvocinia and other Infusoria. He found that as a 
rule when solutions of neutral substances are sufficiently 
concentrated they repel the organisms, and was at first of 
the opinion that the repulsion is simply due to a mechanical 1 
(osmotic) stimulus. Having, however, found exceptions in 
glycerine, peptone and alcohol in addition to acids and alkalis 
he finally 2 attributed the repulsion chiefly, if not entirely, to 
the chemical qualities of the solutions. Massart 3 has since 
made a special study of the action of concentrated neutral 
substances, and has come to Pfeffer’s earlier conclusion that 
the repulsion is usually an osmotic effect. The reaction to 
the mechanical stimulus is known as tonotaxis or osmotaxis. 
Massart made investigations upon a variety of subjects 
including Bacteria, marine organisms, the muscles of frogs 
and human eyes. He came to the conclusion that the repul¬ 
sion of Bacteria, &c. from neutral salts (when this takes place) 
is solely due to a negative tonotactic stimulus. Some or¬ 
ganisms, however, e. g. Bacterium termo , appear to be quite 
insensitive to the effect of concentration. 
The relation between stimulus and reaction for chemotaxis 
has been determined by Pfeffer 4 to be that given in Weber’s 
Law. Although this law has been verified 5 for a tonotactic 
1 Pfeffer, loc. cit, Bd. i, pp. 455, 480. 2 Bd. ii, pp. 623, 624, 659. 
3 Massart, Sensibilite et adaptation des organismes a la concentration des 
solutions salines, Arch, de Biologie, t. ix, 1889. 
4 Loc. cit., Bd. i, pp. 395-408. 
5 Rysselberghe, Reactions osmotiques des cellules vegetales a la concentration 
0 0 2 
