80 



Comparative Animal Physiology 

 TABLE 9 (continued) 



CONCENTRATION OF IONS IN SEA WATER AND IN BODY FLUIDS 

 For sea water, in mM/1.; in body fluids, in mM/1. (except where stated as mM/1. H2O) 



Hydrogen Ion Concentration. Animals maintain a relatively constant 

 hydrogen ion concentration which is usually more acid than the medium 

 (Table 10). Sea water is alkaline (pH 8.0 to 8.1), whereas the blood and 

 body fluids of marine animals have a pH usually between 7.2 and 7.8. Fresh 

 water is also for the most part alkaline, although in some swamps and bogs the 

 water may be more acid than the blood of inhabitants. Willmer ^-'^ found 

 the blood of some South American fish to have a similar hydrogen ion con- 

 centration, whether the fish came from rivers (pH 6.7) or from acid swamps 

 (pH 3.8—5.0). No data are available on the pH of gastrotrichs and other 

 invertebrate inhabitants of acid swamps. A few representative pH values for 

 insect bloods are given in Table 10; most insect bloods are unique in being 

 slightly acid. A tabulation of the pH values for 72 species of insects gives only 

 fourteen values higher than pi I 7.0. Land vertebrates have a blood pH usually 

 near 7.4. 



Ionic Regulation. The ability of an aquatic animal to adjust to the medium 

 or to regulate the concentration of a particular element is indicated by the ratio 

 of the concentrations inside to the concentrations outside the body (1 able 11). 



