76 Thirtieth Annual Meeting 



trout have access to tlie eartli, or wliere the pond is filled witli an 

 abundance of vegetation, while this is not exactly a cvire for 

 disease, it nuiy prevent it, and yet he prescribes as a remedy that 

 Ave build cement ponds. This of course would cut off access to 

 the earth and prevent the growth of vegetation, and while this 

 might cure some particular form of disease or destroy some par- 

 ticular kind of parasite, might it not also encourage the develop- 

 inent of other })arasitic forms which the presence of vegetation 

 would have a tendency to correct or prevent ? 



Prof. Marsh : It is a matter of experience that earth ponds 

 actually did prevent the disease. That is, at a particular station 

 the disease was in existence in a small pond, say an eighty foot 

 pond lined with wood in the ordinary way; a great many of the 

 fish were dying there every day; and the prosjiect was that in a 

 short time they would all be dead; but we took them and ]nit 

 them into one of these large natural ponds which had been dug 

 out. hut which contained no wood, cement or stone in it, and the 

 vegetation grew much as in an ordinary pond. It had all varie- 

 ties of temperature, ))eing fed with springs, and near the sjjrings 

 the fish could get as cool as they pleased, while at the top of the 

 pond the water was as warm as could he desired, and there was a 

 variety in temperature. These trout did not all die and the 

 disease was checked. I do not think the earth cured any of them 

 that already had the disease but it stopped tlu' spread of the 

 disease. The disease had existed in a pond not much larger than 

 this room, and there was ev;>ry chance for the disease to spread; 

 but when the Hsh wcMX' ])ut in the large pond they were widely 

 separated and while there were fish that had the disease, no 

 doubt, yi't they did not pass it on to the rest and they got well. 

 XoAV if that could be applied at all the stations where this 

 disease is found and the fish eo\dd ))e turned over into such 

 ponds, it would work well at least for a time, but, as 1 said in the 

 pa pel-, the infection even of such a large pond as is mentioned is 

 merely a matter of time in my opinion. When the mud at the 

 bottom of the largt' pond once l)ecomes impregnated with the 

 germs that have been cai-ried over, the large ponds instead of 

 cliecking the disease will spread it, and when you do get one of 

 those laig'e ])onds infected you will never get the infection out; 

 it is much harder to disinfect the large ponds than the small 



