THE DUCK SICKNESS IN UTAH. 15 
THE CAUSE. 
In the course of the investigations it has been established definitely 
that the duck sickness in Utah is caused by the toxic action of certain 
soluble salts found in alkali. In other words, it may be said that it is 
due to poisoning by alkali, as that term is used in the West. By 
actual experiment it has been found that the duck sickness may be 
caused by the chlorides of calcium and magnesium. Experiments 
have indicated that other salts may be incriminated in Utah and 
elsewhere, but this statement is made with reserve, as it has not yet 
been definitely established. 
The Salt Lake Valley is well cultivated and productive and owes 
its fertility almost entirely to irrigation. In the last 15 years the 
amount of arable land actually under water has greatly increased, and 
the stream flow at the river mouths has correspondingly decreased. 
In midsummer of ordinary years little or no water now passes the 
irrigation dams on Bear River. The water found at that season in 
the lower channels comes from such small tributaries as enter below 
the dams and from seepage from water used in irrigation. Practically 
the same condition holds in the other streams that flow into Great 
Salt Lake. Thus irrigation has decreased the amount of water sup- 
plying the marshes on the lake front, and the resulting slow drainage 
induces stagnation over large areas. After June 15, as the spring 
waters in Bear River recede, great expanses of mud flat are laid bare 
in the sun. Surface evaporation and capillary attraction rapidly 
draw the salts held in solution in the mud to the surface and there 
concentrate them. As the mud becomes drier these concentrates are 
visible as a white deposit or scale (efflorescence) . This in many cases 
is exposed only an inch or so above the surrounding water level 
(PI. I, fig. 2). In the large bays strong winds bank up the water and 
blow it in across these drying flats. As it advances it takes rapidly 
into solution the soluble salts, largely sodium chloride, but containing 
calcium and magnesium chloride also. This inflow of water carries 
with it quantities of seeds and myriads of beetles, bugs, and spiders, 
washed out of crevices and holes in the dried and cracking soil. The 
ducks come in eagerly to feed on this easily secured food and work 
rapidly along at the front of the advancing water, each bird hurrying 
to get his fill. Many individuals in this way secure a sufficient 
quantity of these poisons to render them helpless. As the water 
recedes again small pools are left in shallow depressions, and other 
ducks and shorebirds feeding in these are affected. 
When this phenomenon was understood the writer was able in 
many cases to predict that with certain strong winds sick birds 
would occur in numbers in certain localities, and after a proper 
interval to send out and have them brought in to the laboratory. 
The alkaline deposits at the mouth of the large channel known as 
Brown's Overflow were specially strong in the chlorides of mag- 
