OXYGEN SUPPLY OF CERTAIN ANIMALS 295 



who set nets in the hypolimnion and rarely caught anything. 

 The migration is due to the decrease of dissolved oxygen and 

 the increase of carbon dioxide. The same investigators also 

 showed that fish could not live for any great length of time in 

 the stagnated region. They caught fish in the epilimnion, 

 placed them in wire cages and then lowered the cages below the 

 thermocline. They found that the fish died in about two hours, 

 presumably from suffocation. However, there are animals in 

 Lake Mendota (Juday, '08) which do not migrate from the 

 stagnant, deeper water. Some of these even lead a rather active 

 life throughout the stagnation period, in the soft bottom mud 

 and in the water above it. 



With these facts in mind, such questions as the following are 

 suggested: How do these animals live? Do they use free oxygen 

 during the stagnation? If so, where do they get it? Do they 

 store it up or manufacture it? If so, how? 



The solution of the problems raised was suggested by Dr. 

 A. S. Pearse, to whom I am indebted for valuable suggestions 

 and aid throughout this investigation. I am also mdebted to 

 President E. A. Birge and Mr. C. Juday for advice and for the 

 opportunity to use certain limnological apparatus. Helpful 

 suggestions have also been received from Dr. M. F. Guyer, 

 Dr. W. J. Meek, Dr. A. S. Loevenhart, Dr. W. S. Marshall, 

 and Dr. S. Tashiro. To Dr. G. H. Bishop I am indebted for 

 help in the construction of apparatus. 



REVIEW OF LITERATURE RELATING TO THE PHYSIOLOGY OF 

 ANIMALS IN AN OXYGEN-FREE ENVIRONMENT 



As early as 1804 Spallanzani showed that 'infusorial ani- 

 maculae' could thrive when their oxygen supply was reduced 

 to the minimum, and that they continued to give off carbon 

 dioxide even when oxygen was entirely cut off. But, being 

 contemporaneous with Lavoisier's notable work on oxidation, 

 Spallanzani's experiments received little notice and the dis- 

 coveries of Pasteur ('61) came as a revelation to physiologists 

 who had generally believed that molecular oxygen was absolutely 

 necessary for the metabolism of all organisms. 



