Abstract
Summary and Conclusions
(1) The anesthetic M.S.222 in 1/3,000 concentration in spring water has no effect on the motility or the fertilizing power of frog spermatozoa. (2) Frog's eggs fertilized in this anesthetic and allowed to remain for 1 hour will develop as well as do the controls. Exposure for longer periods will show an increasing percentage of abnormal embryos. (3) Embryos that show muscular activity (stage 19 and older) are completely immobilized (except for ciliary activity) within 80 seconds at ordinary laboratory temperatures, some embryos becoming quiet within 30 seconds. Recovery rate (i.e., the return to muscular activity) ranges from 4 to 14 minutes, depending more on the stage of development than on the duration of anesthetization. (4) Prolonged exposure to the anesthetic produces abnormal embryos if the exposure is made prior to neurulation and kills the embryos at stage 25. This latter instance may be due to the change in the respiratory mechanism at that time. (Urodele larvae do not show this reaction, and may be anesthetized at least up until metamorphosis.) (5) The anesthetic has no effect on ciliary action but is quick in its effect on muscular activity; it is non-toxic in the dilution of 1/3,000 in spring water for periods adequate for surgical operations; and recovery time is uniformly brief. M.S.222 has proven to be a very satisfactory anesthetic for amphibian embryos.
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