Two types of non-nitrogenous products may be expected: The aliphatic amino-acids give rise to ammonia and fatty acids; these form calcium salts which break down to calcium carbonate. The aromatic amino-acids--tyrosin, phenylalanine, etc.--which would account for about 6 per cent. of the nitrogen of vegetable proteins, would be expected to give ammonia and phenolic substances. Now phenols are poisonous to plants and if no method existed for their removal the accumulation would ultimately render the soil sterile. Matters would be even worse on cultivated soils, since cows’ urine, which enters into the composition of farmyard manure and is the chief constituent of liquid manure, contains, according to Mooser, no less than 0·25 to 0·77 grams of _p_-cresol per litre,[I] a quantity three to ten times that present in human urine. Fortunately this contingency never arises, for the soil contains a remarkable set of organisms capable of decomposing the phenols and leaving the soil entirely suitable for plant growth. This affords an interesting case of an organism--in this case the plant--growing well in a medium in spite of some adverse condition, not because it is specially adapted to meet this condition, but because some wholly different agent removes it. [I] Mooser, Zeitschrift physiol. Chem., 1909, lxiii., 176. No phenol was found. It is possible that the _p_-cresol is not entirely derived from the protein, but that some comes from the glucosides in the animals’ food. Other ring compounds, e.g. pyrrol, arise in smaller quantity in the decomposition of protein, but their fate in the soil is not known. We may summarise the probable changes of the protein as follows:-- Protein. +-------------------+------------------+ | | | Aliphatic Aromatic Other amino-acids amino-acids compounds | | (Pyrrol, etc.) +--------+--------+ +--------+--------+ | | | | Fatty acids and Ammonia Phenolic hydroxy acids | compounds | Nitrite | | | | | | | ↓ ↓ ↓ Calcium Nitrate CO₂ carbonate