| hypophysectomy, chemical | Total or subtotal destruction of the pituitary gland by chemical injection. It is usually achieved by injection of ethyl alcohol via trans-sphenoidal cannulation under stereotaxic control. It is usually performed for the treatment of intractable pain. (12 Dec 1998) |
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| defoliants, chemical | Herbicides that remove leaves from trees and growing plants. They may be either organic or inorganic. Several of the more persistent types have been used in military operations and many are toxic. (12 Dec 1998) |
| sympathectomy, chemical | Sympathectomy using chemicals (e.g., 6-hydroxydopamine or guanethidine) which selectively and reversibly destroy adrenergic nerve endings while leaving cholinergic nerve endings intact. (12 Dec 1998) |
| evolution, chemical | Chemical and physical transformation of the biogenic elements from their nucleosynthesis in stars to their incorporation and subsequent modification in planetary bodies and terrestrial biochemistry. It includes the mechanism of incorporation of biogenic elements into complex molecules and molecular systems, leading up to the origin of life. (12 Dec 1998) |