The Comb of the Baby Chick as a Test for the Male Sex Hormone

Abstract

This work is a continuation of that already reported 1 on the use of comb growth in white leghorn chicks for the assay of male sex hormone activity. The method previously employed involved the daily application of 0.1 cc of sesame oil, containing crystalline androsterone, to the region of the comb; the chicks were-started on the 6th day after birth, treatment was continued for 10 days, and the combs were excised and weighed on the 17th day; the total dosage varied from 0 to 500 gamma, which corresponds to 0-50 gamma per daily application. In all of these experiments, there occurred a progressive increase in comb weight with dosage of androsterone, but the graphs were highly irregular and curved toward the dosage axis as if they might reach plateau values beyond 500 gamma. The chief aim of the present work was to determine what changes in the experimental conditions previously employed must be made in order to effect: (1) An increase in uniformity of the comb growth response of any one group of chicks treated simultaneously with the same quantity of hormone, this uniformity being measured by the standard deviation of the mean for the entire group. (2) An increase in sensitivity of the reaction, as measured by the mean difference in comb weight per unit weight of androsterone throughout the entire range of dosage employed.

To attain this objective, it has been found desirable to introduce the changes in procedure indicated in Table I.

The use of younger chicks and the reduction of the period of application of the androsterone resulted in a marked increase in uniformity of the data; an improvement likewise resulted from the reduction in volume of oil used as vehicle, presumably because of diminished loss by spreading beyond the comb area. The sensitivity of the reaction was increased considerably by reducing the dosage range as indicated.

In all, 5 independent series of experiments have been performed, the number of chicks in any one series varying from 70 to 204. With one exception, each series was made up of 6 groups of chicks, each group corresponding to a different dosage value from 0 to 50 gamma inclusive. The final data were plotted as mean comb weight for all the chicks of any one group against the dosage for that group. The graph for any one series approximates a straight line, although the degree of approximation is not as good for the series based on less than 100 chicks as it is for the larger series (Fig. 1).