104 



Scientific Proceedings (112). 



It should be stated that monsters rather similar to those 

 induced by the increased oxygen have resulted also from treat- 

 ment with reduced oxygen pressures and these have all been 

 produced in embryos aged 2 days or less at the time of treatment. 

 However, some of the abnormalities of the types mentioned 

 above are practically absent in series of embryos treated with 

 reduced oxygen. That the monsters are in fact induced by the 

 altered oxygen pressures is adequately shown by our complete 

 data. These data are the result of 80 experiments upon nearly 

 2,000 embryos of various but precisely known ages, with oxygen 

 concentrations varying from 8.0 to 96.5 per cent., and with dura- 

 tion of treatment extended from 8 hours to 10 days. 



In older embryos subjected to increased oxygen the normal 

 amount of hemoglobin is decreased, as indicated by macroscopic 

 examination, and quantities of it appear in solution in the amniotic 

 fluid. Quantitative studies of the changes in the blood pigment of 

 embryos subjected to decreased and increased oxygen pressures 

 may be made later. 



During the various stages of its development the embryo 

 utilizes three different respiratory surfaces and these are further 

 associated with from none to several of the usual compensatory 

 mechanisms. Age therefore becomes the chief factor involved in 

 the death or survival of embryos subjected to altered oxygen 

 pressures. This fact is sufficiently shown in Table II. The data 

 of the table also indicate that longer periods of exposure are more 

 lethal than are 24-hour periods; adequate compensatory changes 

 are usually limited to definite stages or ages of the embryo. Tests 

 have shown that the adult bird readily survives 24-hour periods 

 in either 10 per cent, or 95 per cent, oxygen. 



Embryos of 8-10 days and older are like hatched individuals 

 in being able to survive the highest percentages of oxygen. The 

 youngest stages best survive decreased pressures of oxygen; for 

 this stage the oxygen may be reduced to 9-10 per cent. (24 hours). 

 It is clear, however, that this "cold-blooded" stage of the bird 

 embryo is unable to reduce the oxygen demands of the tissues to a 

 further reduction of the oxygen supply. 



Although the age of the embryo is the most important factor in 

 its capacity to survive an altered pressure of oxygen the data of 



