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D

Detergent

a chemical that disperses and removes soil, organic material and greasy residue from surfaces as well as reducing surface tension and increase the penetrating ability of water. This is a process that is important in allowing disinfectants to penetrate the pathogens underneath. Some disinfectants have their own detergent properties (eg the halogens – bleach and iodine, quaternary ammonium compounds).

Developer

a chemical solution which converts exposed silver bromide crystals into silver metal within the emulsion during processing

Diarrhoea

production of faeces that contain an excess amount of water


Diastema

a space between teeth. There is a natural space in the jaw of rodents and herbivores where canine teeth would be found in other species.


Diastole

relaxation stage of the cardiac cycle. The term applies to both atrial and ventricular relaxation.


Diffusion

the net movement, as a result of random motion of its particles, of a substance from an area of high concentration to an area of low concentration


Digestion

the process by which food materials are broken down into small soluble chemical units


Diploid cells

cells with the full number of chromosomes, each in pairs. These include most cells within the animal’s body.


Diploid number

the number of chromosomes (2n) found in the nucleus of all cells except gametes which are haploid cells


Disinfectant

a chemical used to control, prevent and destroy pathogens present on inanimate objects - although it is not usually active against bacterial spores. The process does not necessarily kill all micro-organisms, but reduces then to a level acceptable for a defined purpose, for example a level which is considered not harmful to health. (Note, the difference between “disinfectants” and “antiseptics” which are applied to living tissues.)



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