Abstract
In previous papers1, 2 a new method was described for evaluating the efficiency of germicides by testing them for their effect on the growth of living embryonic tissue and on bacteria. A number known as the toxicity-index was determined which was defined as the ratio of the highest dilution of disinfectant that showed no growth of embryonic tissue in 48 hours to the highest dilution required to kill the test-organism in 10 minutes. Theoretically the smaller the index the more nearly perfect the germicide.
The present method attempts to control several variables which were not considered in the previous work. These are: (1) performing all tests at 37°C. instead of at 25°C; (2) keeping the time of action of germicide on tissue and bacteria the same, viz., 10 minutes; (3) conducting all tests in the presence of a definite amount of organic matter.
Efecct of Gernzicide on Tissue. Chick hearts are removed from 10-12-day-old embryos and minced into fragments about 0.5 mm. in diameter. The fragments are suspended in Tyrode's solution, about 100 pieces per cc. One-half cc. of suspension is pipetted into each of a series of tubes containing 2.5 cc. of a mixture of 3 parts embryonic extract∗ and 1 part defibrinated horse serum. The tubes are placed in a 37°C. waterbath.
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