226 FARMYARD MANURE 



little changed or broken down to a considerable extent 

 into simple compounds. 



The putrefactive decomposition which begins in the 

 intestines of the animal is continued in the manure heap : 

 its nature and the organisms which carry out the work 

 have been discussed in a previous chapter (pp. 100-1 14), 

 which should be referred to again in this connection. 



Ex. 108. Take 5 or 10 grams of fresh manure of the horse, 

 cow, and pig. Shake each portion in a flask containing 200 c.c. of 

 sterile water: transfer 10 c.c. of the turbid liquid to another 

 similar flask containing 200 c.c. of sterile water. From this 

 second flask inoculate a tube of gelatine or agar medium and 

 transfer to Petri dish. Incubate at 20 to 25 C. : note the kind 

 of colonies obtained and examine the organisms producing 

 these. Prepare pure cultures of those which appear to be dis- 

 tinct. Cultivate in various media and endeavour to determine 

 their species, comparing with authentic pure cultures of B. coli, 

 B. aerogenes, Proteus sp., B. fluorescent ^ etc. 



Ex. 109. Repeat the above experiment, using old decayed 

 manure. 



(iii) Nitrification and Denitrification. The nature ot 

 both these processes and the bacteria to whose activity 

 they are due have already been treated in detail 

 previously (see pp. I 35-168). Under ordinary conditions 

 little nitrification occurs in the manure heap except per- 

 haps in the outer layers, and it is not until the manure has 

 become incorporated with the soil that its nitrogenous 

 compounds become rapidly changed into nitrates. 



(iv) The Fermentation of Cellulose. The solid fabric 

 of the body of a plant consists chiefly of cell-walls, which 

 in the main are composed of a carbohydrate termed 

 cellulose, having the empirical formula C 6 H 10 O 5 . It is 



