110 



motile organs are withdrawn into the substance of the 

 spore, and small root-like outgrowths appear at the at- 

 tached end of the spore and hold the latter in place as 

 well as absorb the nourishment from the substratum. 

 These spores, then, are not only able to swim about in 

 stagnant water (to say nothing of being disseminated 

 by flowing water) and to select a suitable place for 

 development, but having found such a place, they are 

 maintained in position by the firm attachment of their 

 roots which are capable of penetrating not only the 

 slimy skin of a fish, but even the hard shell-like coating 

 of an insect. It is these spores mainly with which we 

 have to contend. For, although the fungus forms 

 another sort of spore, the latter is produced in much 

 smaller numbers and does not immediately develop into 

 a plant. The spores described above (known techni- 

 cally as " zoospores," from their animal-like habit of 

 swimming about) are the sort which, from their num- 

 ber, rapidity of growth and motility, enable the plant 

 to develop in enormous numbers and to become widely 

 disseminated during a single season. 



The fact that these zoospores are not covered by 

 any sort of protecting skin or membrane gave rise to a 

 hope that they might be destroyed to a greater or less 

 extent by the addition of a disinfecting or germicidal 

 substance to the water containing them. The choice 

 of disinfectant was naturalh' limited to sub.stances which 

 would not injure the fish. It seemed, on the whole, 

 best to try the effect of " electrozone," an exceedingly 

 powerful germicide formed by the passage of an electric 

 current through salt water. Electrozone can be swal- 

 lowed without danger and seemed likely to be the best 

 disinfectant to add to the water. 



The first step in the experiment was to determine 

 what proportion of electrozone the water must contain 

 in order to stop the development of the fungus. To 



