135 
swarmspores of Aethalium septicum. Stange declares 
that these are positively chemotactical as regards the 
following free acids: lactic acid, butyric acid, valeric acid, 
propronic acid, malic acid and tartaric acid. Kusano, on 
the other hand, thinks the swarmspores positively chemo- 
tactical for nearly all acids. He sees the explanation of 
these various results in the fact, that Stange used much 
narrower tubes than he did. To make this clear, he gives 
a list (page 38). Capillary tubes with a diameter of 10 to 
240 » were all filled with !/,, normal solution of mono- 
kalium phosfate and put into à preparation of Aethalium 
swarmspores. After 5 or 10 minutes in the tubes of 100 
or still smaller diameter there was nothing or very little 
to be seen of a positive reaction, while in the wider tubes 
a distinct reaction could be seen. Knowing moreover, 
that Stange worked with capillary tubes, which had a 
diameter of 13—15 , we can easily understand the various 
results of Stange and Kusano. Remembering that, the 
bigger the diameter becomes, the more diffusion plays a 
part and that by this during the experiment the concen- 
tration of the chemotacticum in the capillary tube must 
really change, we shall see that also the defining of a 
threshold with the capillary method has great drawbacks. 
Kusano, in his investigation, gives us a clear repre- 
sentation of this (page 69). He works as follows. By 
bringing the swarmspores into acid-solutions of various 
concentrations, he fixes the minimum-concentration of every 
acid, by which action all swarmspores immediately are at 
rest and contract themselves, in consequence of the 
injuring action of the acid. On page 60 we find a table of 
this When comparing these concentrations to those of 
the acid-solutions, which he has to do in the capillary 
tubes to obtain a just visible accumulation at the mouth, 
it appears that these concentrations are far more injurious 
than the solutions of page 60. 
