REFLECTIONS ON DISEASE TREATMENT 169 
heap is then covered with tarpaulins or sacks sprayed 
with formaldehyde, and left so covered for 48 hours, 
after which time the covering is removed and the heap 
opened out to dry. This is accelerated by constant 
turning, but all instruments should be sterilized with 
formaldehyde to prevent reinfection of the heap. When 
the soil ceases to smell of formaldehyde it is ready for 
use. 
Benches, staging, boxes, and pots may also be 
sterilized by thoroughly wetting with the solution, 
stacking, and covering for 48 hours, and then allowing 
to dry. Where stable manure is suspected of carry- 
ing infection formaldehyde offers the best method of 
sterilizing it. 
_ At Rothamsted many chlorine and nitro-derivatives 
of benzene and the cresols have been tested with excellent 
results. Among these may be noted dichlorcresol, 
orthonitrochlorbenzene, and chlordinitrobenzene, but 
these have not been tested yet on a commercial scale, 
and large quantities are not yet on the market. The 
grower may look forward with confidence to the future, 
when thoroughly efficient chemical sterilizers will be 
available. 
Sterilization by Drying 
The fact that some soil organisms can resist desicca- 
tion to a greater degree than others is responsible for the 
fact that the drying of soils produced effects similar to 
those of partial sterilization. Under normal conditions 
of cultivation, however, it is possible that glasshouse soils 
are never sufficiently dry to benefit from this process. 
The Effect of Different Methods of Soil Sterilization 
upon Plant Growth 
Sterilization of the soil results in the liberation of 
plant foods previously locked up in unavailable forms and 
in an increased production of ammonia. Plant growth, 
