STUDIES IX THE EXPHEDEEXTAL AXALYSIS OF SEX. 59-3 



them evei'y day with about 3 c.c. In all cases rather more 

 extract was administered in my experiments in a given time 

 than in Dr. Walker's. Since Dr. Walker obtained pronounced 

 effects in three weeks, and very pronounced effects in less 

 than two months, I have not continued the injections for 

 more than a month except in a few cases. That this does not 

 vitiate my results is, however, most clearly shown by the fact 

 that in the two birds in which very mai-ked variations in the 

 comb were observed, comparable to Dr. Walker's, the full 

 increase took place three weeks after the first injection, the 

 injections being performed at intervals of two or three days. 

 The injections were made with aseptic precautions in the 

 pectoral muscles. In measuring the comb two methods have 

 been used : firstly, by tracing an outline of the comb onto 

 cardboard, and secondly, by measuring the two greatest 

 dimensions of the comVj directly with a pair of compasses. 

 Both methods were used with the four birds in Experiment 1, 

 but the numbers given in referring to this exjDeriment in the 

 schedule at the end were all taken from the tracings, as the 

 direct measurements did not form a complete series for all the 

 birds. As a consequence of this the numbers referring to 

 comb measurement in these birds do not vary so smoothly as 

 in the case of the later experiments. In Experiments 2 and 

 •3, relating to fifteen birds, I relied entirely on direct measure- 

 ments, which I consider liable to less experimental error. 

 Measurements were not made of the wattles, as being too 

 inconvenient. In calculating the percentage increase the 

 following method is used. The height of the comb multiplied 

 by the length, the same points being, of course, always taken, 

 is considered as giving roughly the area of the comb. The 

 increase of area observed is calculated as a percentage on the 

 original area when the experiment began. Thus in Bird Xo. 1 

 the original area was 50 x 25 ; the area at the end of the 

 injections was 72 x 37, whicli gives, as the percentage 

 increase — 



(72 X 37) - (50 X 25) x 100 



^ ^ — ^^ = 11 o per cent. 



50 X 25 ^ . 



