The contents of this Schools Encyclopedia has been organised by subject. There are 5500 articles, some of which have been listed under several subjects. The general principle has been that this subject index should be helpful rather than categorising. So for example Pluto is still listed in the category of planets even though it is not considered a planet any more and Russia as a country has been included in both Europe and Asia. People are often listed both in the biographies (of which there are 850) but also under the area of study for which they were famous. If you struggle to find a particular article we suggest you try the title index which includes every word of the title of every article (including alternative titles, so Pyrites are listed under Pyrites, Fool and Gold). Most topics related to the natural world, including a lot of information on birds, plants, dinosaurs, medicine, insects and so on are under Science / Biology. This classification was done by hand so please report errors.