272 CHYMISTRY APPLIED TO AGRICULTURE. 



When the water of wells is supplied by living streams, or 

 when the ground around them is paved, or consists of beds 

 of stone or hard clay which will not allow the water to fil- 

 trate through, the precautions which I have suggested are 

 not so absolutely necessary ; but these circumstances rarely 

 occur in the country. 



Cistern-water would be purer and more wholesome than 

 any other, if the roofs, eave-troughs, and basins, could be 

 kept perfectly clean; but the filth deposited by pigeons 

 and other birds upon the roofs, is carried by the rain into 

 the reservoir, and renders it disagreeable to drink, though 

 it is not absolutely unwholesome : this I have observed to 

 be the case upon the most elevated table lands of our moun- 

 tains, where the inhabitants have no other resource for 

 procuring the water necessary for domestic purposes. I 

 have also observed, when care was taken to cleanse the 

 troughs and reservoirs frequently, and to conduct the first 

 portions of the rains into pools, for the use of the animals, 

 so as to receive only that portion which fell upon the roofs, 

 after they had been well washed, that this water could be 

 kept throughout the year, and that it furnished a drink 

 equally healthy and agreeable. 



In most districts, the water of pools forms the only re- 

 source for supplying the wants of animals ; and when these 

 become dry, during the summer, the animals must often be 

 driven a considerable distance to procure necessary drink. 

 In order, therefore, to prevent the water of pools from filtrat- 

 ing into the ground, and likewise to preserve it sweet, the 

 bottoms of pools should be paved. 



In spite, however, of all the precautions which can be 

 taken, it is almost impossible to preserve the water in pools 

 from deterioration : the excrements of animals, and the 

 dirt from their feet, as well as the plants which always 

 spring up in stagnant water, very soon change its color 

 and its nature; it becomes green and thick, and to man, 

 disgusting : fortunately, animals are less delicate, and 

 can accommodate their inclinations very well to drink of 

 this kind: it is even said, that when accustomed to it, they 

 prefer it to the purest and most limpid stream. Such wa- 

 ter rarely produces any bad effect ; the filth which is mixed 

 with it is slow in decaying, and the plants which spring 

 up, contribute to its healthfulness, and thus we rarely per- 

 ceive from them that fetid odor which indicates putrefac- 

 tion. The greatest fault in pond-water, is its temperature 



