It is clearly recognized by the farmers that mud collected from those sections of the canal leading through country villages, such as that seen in Fig. 10, is both inherently more fertile and in better physical condition than that collected in the open country.  They attribute this difference to the effect of the village washing in the canal, where soap is extensively used.  The storm waters of the city doubtless carry some fertilizing material also, although sewage, as such, never finds its way into the canals.  The washing would be very likely to have a decided flocculating effect and so render this material more friable when applied to the field.

One very important advantage which comes to the fields when heavily dressed with such mud is that resulting from the addition of lime which has become incorporated with the silts through their flocculation and precipitation, and that which is added in the form of snail shells abounding in the canals.  The amount of these may be realized from the large numbers contained in the mud recently thrown out, as seen in the upper section of Fig. 95, where the pebbly appearance of the surface is caused by snail shells.  In the lower section of the same illustration the white spots are snail shells exposed in the soil of a recently spaded field.  The shells are by no means as numerous generally as here seen but yet sufficient to maintain the supply of lime.

Several species of these snails are collected in quantities and used as food.  Piles containing bushels of the empty shells were seen along the canals outside the villages.  The snails are cooked in the shell and often sold by measure to be eaten from the hand, as we buy roasted peanuts or popcorn.  When a purchase is made the vender clips the spiral point from each shell with a pair of small shears.  This admits air and permits the snail to be readily removed by suction when the lips are applied to the shell.  In the canals there are also large numbers of fresh water eel, shrimp and crabs as well as fish, all of which are collected and used for human food.  It is common, when walking through the canal country, to come upon groups of gleaners busy in the bottoms of the shallow agricultural canals, gathering anything which may serve as food, even including small bulbs or the fleshy roots of edible aquatic plants.  To facilitate the collection of such food materials sections of the canal are often drained in the manner already described, so that gleaning may be done by hand, wading in the mud.  Families living in houseboats make a business of fishing for shrimp.  They trail behind the houseboat one or two other boats carrying hundreds of shrimp traps cleverly constructed in such manner that when they are trailed along the bottom and disturb the shrimps they dart into the holes in the trap, mistaking them for safe hiding places.