294 L. H. HYMAN. 



easily obtained. Brom cresol green was not found to be reliable 

 and consequently pH 5.0 could not be determined very exactly. 

 The acids employed were: hydrochloric, nitric, sulphuric, 

 carbonic, acetic, butryic, citric, and tartaric. Each of these 

 acids was used in the following concentrations, in terms of pH: 

 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, and in some cases 4.5. At least three 

 experiments at each concentration of each acid were performed 

 and in many cases a greater number of trials was deemed neces- 

 sary. It will be seen that the amount of labor involved was very 

 great and this fact must serve as my excuse for any deficiencies 

 in the investigation which may suggest themselves to the reader. 



EXPERIMENTS WITH MARINE ANIMALS. 



The experiments recorded in this section were performed in 

 1922 at the Hopkins Marine Station, Pacific Grove, California. 

 The animals used were two species of starfish, Leptasterias 

 equalis, and Patiria miniata, and the nudibranch, Anisodoris 

 nobilis. It may be noted in passing that starfish and nudibranchs 

 have been found to constitute very favorable material for 

 respiratory experiments. 



The animals were placed in wide-mouthed salt bottles and 

 the tests carried out as outlined above. Leptasterias is a small 

 species and several individuals were therefore used in each bottle. 

 As the other two species are larger, generally only one individual 

 was necessary. Generally two successive trials of the oxygen 

 consumption in normal sea-water were carried out. The sea- 

 water was then acidified to the desired amount with hydrochloric 

 acid and a determination immediately carried out. The animals 

 were then usually allowed to stand for two to several hours in 

 the acidified sea-water; another test was then performed. The 

 animals then remained in the acid water over night, about 13 to 

 15 hours in different experiments, whereupon a third test of the 

 respiration in the acidified water was performed. The animals 

 were then returned to normal sea-water, and after several hours 

 the oxygen consumption was again tested in normal sea- water. 



It should be understood that for each test freshly aerated and 

 freshly acidified water was used. The water was brought in 

 directly from the ocean as the sea-water coming through the 



