EXPERIMENTAL EVOLUTION. 141 



ditions of avian development and reproduction. The more important 

 of his results are the following : 



It has been found that the failure of some birds' eggs to hatch is 

 caused by a hitherto unsuspected and quite unapparent uiadequacy of 

 the egg-shells. Shells which do not break may, nevertheless, pemiit a 

 too rapid ingress of oxygen and egress of water, and this certainly 

 results in the death of many embryos. Undoubtedly this discovery, 

 w^hich is of much interest in our sex and fertility studies, will become 

 of real importance in the poultry industry, where probably millions of 

 incubated eggs with failing embryos are annually lost from this source. 



Two attempts have been made to learn a treatment for birds which 

 produce eggs with defective or inadequate shells. These attempts have 

 been essentially unsuccessful in the main purpose, but have developed 

 some useful facts. In collaboration with Mr. Martin C. Hanke, it 

 was found that the feeding of additional soluble calcium salts — calcium 

 lactate and calcium phosphate — affects but very slightly the amount 

 of calcium which laying doves utilize in the formation of the egg-shell. 

 It is concluded that the inadequate shells are probably not primarily 

 due to a Lack of soluble-calcium compounds in the food of the bird. 



In view of the above result, it was thought advisable to investigate 

 the mechanism of control of the oviducal secretions of the bird. With 

 the assistance of ]Mr. Cecil V. King, the effects of atropine, nicotine, 

 and cocaine upon the production of albumen and shell-material was 

 extensively studied. The results lend no hope to a possible stimula- 

 tion of excess secretion by means of drugs. An effect (somewhat re- 

 duced secretion) could usually be obtained with appropriate dosage of 

 cocaine and nicotine, but Dr. Riddle concludes that either the oviducal 

 secretions of the bird are largely independent of the sympathetic 

 nerves or that the drugs w^hich act most pronouncedly on these nerves 

 of the mammal do not have an essentially comparable action in doves. 



Finally, in connection with the study of the effects of increased and 

 decreased pressures of oxygen on embryos of the two sexes, Dr. Riddle 

 has completed an investigation of the necessary gaseous environment 

 of avian embryos. In general, it is found that for oxygen the lower 

 limit of life and development, for 24 to 48 hour periods followed by 

 return to normal air, is about 10 per cent and the upper limit about 

 96 per cent. The upper limit for carbon dioxide, in connection with 

 increased pressures of oxygen, is not far from 10 per cent, which is 

 more than 300 times the amount normally present in air. The age of 

 the embryo is an important modifying factor. It has also been found 

 that the higher pressures of oxygen result in the complete disappear- 

 ance of hemoglobin from the blood of embryos of about 2 days of 

 development, and that abnormalities and "monsters" are often pro- 

 duced in embryos of less than 1.5 days. A further study of the condi- 

 tions and nature of these changes is being made. 



