Afuerican Fisheries Society. 69 



abled them to gain tlie footliold in the brood of iisli. Of conrse 

 tlie virnlenee of the organisms is another factor wiiieli enters in. 

 The foothokl is the important thing. Xow, where were these 

 germs before they got inside the front. The air contains many 

 bacteria. But it is the less likely hypothesis that they dropped 

 into the ponds from the air and then found their way into the 

 fish. There is the soil and water, and if either of these it is of 

 course iiltimately the soil. This is a more reasonable supposi- 

 tion. Books on bacteriology have long lists of species of soil 

 organisms. It is readily conceivable that some of these species, 

 in the earth immediately surrounding the springs, conduits, or 

 ponds of a trout hatchery entered the water and lodged within 

 the body of a trout and found its blood and tissues so favorable a 

 lionie, that whether or not it had ever been parasitic before, it 

 now l3ecame so. Tt is readily seen that the mouth would be a 

 probable avenue of entrance. The germ having entered the water 

 is apt to be taken in with food of any sort. It is smaller than 

 most of the Ijody cells and can make its way into tissues between 

 these cells. It can enter through abrasions anywhere on the 

 exterior of the fish, through l:)reaks too small to l)e seen, possibly 

 througli the intact skin. Theoretically one bacterium and one 

 trout are sufficient for the start. The rest is easy. 



It appears probaljle then that the original infection was not 

 present in great abundance, Imt was comparatively dilute. But 

 after occurrence of one epidemic the conditions are very differ- 

 ent. When a brood of trout in a pond is affected with the dis- 

 ease, the specific germs must be thoroughly distributed about the 

 pond. Wooden or earth ponds are pervious. They harbor the 

 germs, and afford a permanent resting place in which they not 

 only live but doubtless multiply, feeding upon the organic mat- 

 ter which is retained from uneaten food and excreta from the 

 fish. The infection is now localized in the pond, it has a focus 

 there, is no longer dilute, but is present in strength, and the fate 

 of the next brood of susceptible fish placed in the ponds is almost 

 a foregone conclusion. These ponds are incapable of tliorough 

 disinfection. 



This brings us to what I may call the wooden ])()nd theory. 

 Wooden, because the ponds have usually wooden linings, but 

 earth or other pervious material comes in the same class with 



