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(sŭ-mā′shŏn) [L. summatio, adding up] 1. A cumulative action or effect, as of stimuli. An organ will react to two or more weak stimuli as if they were a single strong one. 2. In mathematics, the process of adding a sequence of numbers, resulting in a sum.

summative assessment

(sŭ-mā′tĭv ă-ses′mĕnt) In education, the use of standardized testing to grade students on their ability to recall facts or principles.


(sŭn′bŭrn″) Dermatitis due to excessive exposure to the actinic rays of the sun. The rays that produce the characteristic changes in the skin are ultraviolet, between 290 and 320 nm. Some people are more resistant to these rays than others, but the skin will be damaged in anyone who has sufficient exposure.

 PREVENTION: Prolonged direct exposure of the skin to sunlight between 10 A.M. and 3 P.M., when ultraviolet rays are strongest, should be avoided to minimize the risk of sunburn and skin cancer. Clothing should be worn to cover the skin or a sun-blocking agent with a sun protective factor (SPF) of 15 or more should be used (to be reapplied each hour if the person is sweating heavily).

image Sunbathing and sunburn are risk factors for skin cancers, including basal cell carcinoma, squamous cell carcinoma, and melanoma.

 TREATMENT: Cool, wet dressings may be applied to the burned area if the reaction is moderate. For severe sunburn, lukewarm baths with oatmeal or cornstarch and baking soda should be given. Aspirin or other nonsteroidal anti-inflammatory agents may reduce inflammation and pain.


(sun′dow-nĭng) Confusion or disorientation that increases in the afternoon or evening. It is a common finding in patients with cognitive disorders, e.g., older persons with dementia, and tends to improve when the patient is reassured and reoriented.


Eyeglasses that protect the eyes from exposure to visible as well as ultraviolet rays. For optimal eye protection outdoors, wraparound sunglasses or solar shields that block both ultraviolet A and ultraviolet B rays should be worn.

sunrise view

An x-ray of the knee in flexion, taken to highlight the patella and its relation to the femoral condyles, e.g., in evaluations of osteoarthritis. SYN: skyline view.


A substance used as a second line of defense against damage to the skin by ultraviolet rays. It is usually applied as an ointment or cream. SEE: photosensitivity; ultraviolet radiation.

image Sunscreens are much less effective in protecting against the damaging effects of the sun than avoiding midday sunlight and wearing protective clothing and headgear—these are the primary defenses against solar injury. Sunscreens should be reapplied after ...

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