His system divided instruments into two categories: instruments with solid, vibrating bodies and instruments containing vibrating air. Musical instruments are also often classified by their musical range in comparison with other instruments in the same family. This exercise is useful when placing instruments in context of an orchestra or other ensemble. These terms are named after singing voice classifications:  Some instruments fall into more than one category. For example, the cello may be considered tenor, baritone or bass, depending on how its music fits into the ensemble. The trombone and French horn may be alto, tenor, baritone, or bass depending on the range it is played in. Many instruments have their range as part of their name: soprano saxophone, tenor saxophone, baritone horn, alto flute, bass guitar, etc. Additional adjectives describe instruments above the soprano range or below the bass, for example the sopranino saxophone and contrabass clarinet. When used in the name of an instrument, these terms are relative, describing the instrument's range in comparison to other instruments of its family and not in comparison to the human voice range or instruments of other families. For example, a bass flute's range is from C3 to F♯6, while a bass clarinet plays about one octave lower. The materials used in making musical instruments vary greatly by culture and application. Many of the materials have special significance owing to their source or rarity. Some cultures worked substances from the human body into their instruments. In ancient Mexico, for example, the material drums were made from might contain actual human body parts obtained from sacrificial offerings. In New Guinea, drum makers would mix human blood into the adhesive used to attach the membrane. Mulberry trees are held in high regard in China owing to their mythological significance—instrument makers would hence use them to make zithers. The Yakuts believe that making drums from trees struck by lightning gives them a special connection to nature. Musical instrument construction is a specialized trade that requires years of training, practice, and sometimes an apprenticeship. Most makers of musical instruments specialize in one genre of instruments; for example, a luthier makes only stringed instruments. Some make only one type of instrument such as a piano. Whatever the instrument constructed, the instrument maker must consider materials, construction technique, and decoration, creating a balanced instrument that is both functional and aesthetically pleasing. Some builders are focused on a more artistic approach and develop experimental musical instruments, often meant for individual playing styles developed by the builder themself.