Abstract
The purpose of this study is to examine the experimental method used by Kuo 1 , 2 , 3 , 4 , 5 to study development of embryonic behavior in the chick. The conditions under which Kuo's experiments were performed, 1 , 2 were as follows.
The shell of the incubating chick's egg was opened in the region of the respiratory air space, exposing part of the inner shell membrane. This was coated with a thin layer of liquid vaseline to render it transparent. The eggs were then observed daily while they incubated upright on their small ends. The impression is given that the same chick could be observed daily from the 2nd, or earliest day of operation, to the 21st, or day of hatching. Except in one paper 6 in which he reported placing only a spot of vaseline on the membrane above the embryo, Kuo has consistently referred to this original procedure. 1 , 2 Behavior observed under such conditions he has considered normal.
Because we questioned the physiologic soundness of this procedure, limiting as it does the normal respiratory exchange of the chick, experiments were undertaken to determine the chances of viability and normal development in chicks incubating under these and similar conditions. Kuo did not record the number of chicks which hatched or the number which failed to do so.
Three experiments were run. In the first, 72 eggs were incubated and operated exactly as described by Kuo. 1 The inner shell membranes of random groups of these eggs were coated with a thin layer of melted vaseline on the 3rd, 4th, 7th, 8th, or 11th day of incubation. None of these chicks survived more than 6 days; 72% died within 3 days of operation.
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