VIII.] FISH GUANO 237 



extracts, are similarly dried and disintegrated for sale 

 as " meat guano " ; even some forms of dried sewage 

 sludge masquerade under the name of guano. 



Fish guano is manufactured in many places where 

 any considerable fish waste is available. The oil is 

 extracted by heat and pressure, and the remaining 

 material is dried and disintegrated as finely as possible. 

 Considering the very varied origin of fish guano, its 

 composition is remarkably constant : the nitrogen 

 varies between 6 and 9 per cent., the phosphoric acid 

 represents from 13 to 20 per cent, of tri-calcic phos- 

 phate. The fineness of grinding is less uniform ; two 

 classes of fish guano are found : in one of them the 

 material is reduced to a light flufty powder, the other 

 is denser and contains pieces of hard bone up to a 

 quarter of an inch in diameter. This coarsely ground 

 material must be less available, at any rate as regards 

 the phosphates. Fish guanos generally contain a 

 distinct amount of oil which has not been removed 

 in the manufacture ; it has been suggested that more 

 than 3 per cent, should be regarded as detrimental 

 to the value, but this opinion — that the presence of oil 

 delays the decomposition of such manures — has really 

 never been demonstrated. 



Fish guano is a comparatively active nitrogenous 

 manure, since some of the compounds it contains are 

 soluble in water and are rapidly decomposed by bac- 

 teria ; the main constituents are, however, proteins and 

 gelatinoids which resist attack to a greater or less 

 degree. In consequence fish guano shares with the 

 true guanos the property of continuing to yield 

 nitrogen available to the plant throughout the whole 

 growing season, though the range of compounds in fish 

 guano must be regarded as a little less active than 

 those in Peruvian guano. Fish guano has for many 



