STALL-MANURE AND STRAW. 125 



burnt, strong-smelling combinations, tar, ammoniacal 

 gas-water, pyroligneous acid, etc., are likewise gen- 

 erated in large quantity. On the contrary, when the 

 air can freely enter, these offensive gases and vapors 

 combine with more oxygen, and now undergo com- 

 plete putrefaction or combustion ; and the products 

 so eliminated are destitute of smell. This kind of 

 decomposition, which is most analogous to complete 

 combustion, and, like this, takes place with abun- 

 dant air and a proper draught, is called decay. 



Why putrid drainings and putrid manures, when 

 applied to meadows or fields, diffuse at first a pow- 

 erful odor, hn^ lose this smell a short time after- 

 wards, is therefore very simply explained : they lose 

 their odor, because they can now absorb oxygen in 

 any quantity from the air, and from the process of 

 putrefaction can make a further transition into that 

 of decay. 



If moist vegetable or animal tissues lie in a room 

 from which the air is entirely or partially excluded, 

 — for instance, in a cellar which has no ventilation, 

 or in a chest, etc., — then in the undisturbed, damp 

 air a decomposition takes place, consisting partly 

 of putrefaction, partly of decay; — the well-known 

 process of mouldering^ recognized mainly by its 

 close smell and simultaneous production of mould, 

 fungi, and spongy excrescences. By the addition of 

 water, this kind of decomposition may be converted 

 into putrefaction ; by the introduction of a current of 

 air, into decay ; or, lastly, it may be brought entirely 

 11* 



