E. J. Russell and A. Appleyard 417 



5. Moisture is one of these. Action came to a minimum in June 

 when the moisture fell to 10 % by weight of the unmanured soil, and 

 15 % by weight of the dunged soil, or 16 and 22 parts respectively by 

 volume, assuming there was no contraction. 



6. Rainfall is an even more important factor : a shower of rain 

 having a notable effect in starting the decompositions. It seems 

 probable that the dissolved oxygen is an important factor here. 



7. The growing crop exerts a depressing effect, though whether by 

 taking up the dissolved oxygen, by giving out COg, or by some other 

 action, is not clear. 



8. The fluctuations in bacterial numbers are not wholly explicable 

 as functions of the temperature and moisture content. Some of the 

 rises and falls are of the kind obtained during the investigations on 

 partial sterilisation : further work on this problem is in hand in our 

 laboratories. 



(Received January '2%lJi, 1917.) 



