160 Transactions of the South African Philosophical Society. 
cast away instead of employing, tends further in that direction. 
The recent discoveries regarding the functions of bacteria with 
respect to the assimilation of nitrogen in the soil help to convince us 
that the soil is the laboratory where garbage is refined and rendered 
fit for use, and in our war with nature we are only fighting our own 
interests by depriving the soil slowly but surely of what -is indis- 
pensable to it. 
With regard to rust and similar diseases in cereal crops it must be 
remembered that a well-nourished and cared-for child is, other things 
being equal, better able-to resist the attacks of disease than one 
living in a vitiated atmosphere, badly fed, and poorly clad. The 
statistics regarding tuberculosis, for instance, tell an unmistakable 
tale in this respect. As with human, so with plant life: when a 
soil becomes exhausted, and’ the crops are no longer able to draw 
-from it adequate supplies of plant food, they fall an easy prey 
to the diseases which they resisted successfully while the soil 
was in better condition. We hear of grain districts where the 
ravages of rust become more calamitous and more widespread every 
year. The first, or one of the first, of the warnings given by the 
hungry land of its approaching exhaustion should not be despised, 
and the important matter for consideration is not to give the soil 
some fertiliser, no matter what, at haphazard, but to adjust the 
manure to the needs of the soil. 
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