560 Butter.—Contributions to our Knozvledge of the 
therefore, a moderate estimate if we conclude that, excluding 
malates and maleates, malic acid attracts the spermatozoa 
about fifty times more strongly than any of the other 
attracting substances tested. 
As an illustration of the difference in the strength of 
attraction, it may be remarked that I have repeated the 
experiments with potassium tartrate with the greatest care 
on several different occasions, and have never been able to 
determine the least attraction at f x X tfW m °l> while with 
an isomolecular solution of malic acid a strong attraction is 
always found to take place. 
The biological aspect of the above results is interesting. 
The facts certainly support the supposition of Pfefifer already 
mentioned, that a substance containing the negative radicle of 
malic acid is liberated at the bursting of the archegonia, and 
serves to attract the spermatozoa to the oospheres. It is not 
impossible, however, that a supplementary role may be played 
in this phenomenon by other substances or another substance 
such as a tartrate or an inorganic potassium salt. 
There are several arguments against the supposition that 
it is the free acid which attracts spermatozoa to the arche¬ 
gonia. In the first place, Pfeffer 1 could determine no acid 
reaction to be given by the liberated cell-sap when the 
archegonia burst. Secondly, the free acid, even at low con¬ 
centrations, is very toxic for the spermatozoa, for it shortens 
their swarm-period considerably. Thus I found that they 
live about twelve times longer in tap-water than in a solution 
of tap-water containing o-oi gm per cent, malic acid. For 
the purpose of the third argument it is necessary to give the 
data showing the manner in which the stimulus of malic acid 
varies with the concentration. In Table IV: R = repulsion, 
A = marked attraction, a = weaker attraction, R-A = repul¬ 
sion at first quickly followed by strong attraction, o = in¬ 
different. The solutions are given in grams per cent. 
1 Loc. cit., Bd. i, p. 418. 
