surface fluctuates between approximately -1.5° in winter and -0.8° C. 

 in summer. The content of tissue oxide in herring in winter is about 

 double that found in summer (Ronald auid Jakobsen I9U7) . The tissue of 

 Arctic fish has a greater content of oxide than does that of fish of the 

 same species caught in the North Sea (Shewan I95I). These data suggest 

 the possibility that trimethylamine oxide coxxld function to increase 

 osmotic pressure to allow the teleost to live in cold water without the 

 danger of becoming frozen. 



Since the tissue fluids of the teleost are at a lower osmotic 

 pressure than is its sea-water environment, the animal is in constant 

 threat of being dehydrated. Teleost tirine has been shown to be hypotonic 

 to plasma. The teleost conserves water that would go into tbe production 

 of urine by excreting up to 90 percent of its excretory nitrogen through 

 the gills in the form principally of ammonia (Baldwin 19^8) . About one- 

 half of the urinary nitrogen excreted by Lophius piscatorius was trimethyl- 

 amine oxide (Grollman I929) . Using the same animal, Erull and Nizet (l^^k), 

 however, reported that the main nitrogenous constituent in the urine was 

 creatinine. Evidence is also lacking on the permeability of gill tissue 

 to trimethylamine oxide. It has been presumed that the oxide is not 

 excreted via the gills. 



Other marine animals . --.The physiological fiinction of trimethyl- 

 amine oxide in marine invertebrates is not known. Marine invertebrates 

 are generally in osmotic equilibrium with their environment (Florkin 19^9) • 

 These animals apparently maintain this equilibrium by transfer of inorganic 

 salts and water across membranes; therefore, the oxide probably does not 

 have an importeint osmotic function in these animals. 



Fresh-water teleosts .--The depression of the freezing point of 

 fresh water is seldom greater than -0.02*, whereas that for the tissues of 

 the fresh-water teleost is approximately -0.6° (Baldwin I95I) « These data 

 show that the tissues of the fresh-water teleost are at a greater osmotic 

 press\ire than is their environment. Considering the low concentration of 

 trimethylamine oxide in fresh-water fish (tables 2 and 3)* it does not 

 appear that the small degree of osmotic pressure contributed by the oxide 

 could be considered an important function in these animals. 



Nitrogen Metabolism 



Although the origin of trimethylamine oxide is unknown, a number 

 of suggestions have been made that relate the occurrence of trimethylamine 

 oxide in an animal to metabolism of nitrogen- containing compounds. 



Trimethylamine oxide as a product of protein metabolism . --Hoppe- 

 Seyler (1930) has suggested that trimethylamine oxide is the nontoxic end 

 product of protein metabolism. Thus far no metabolic pathway for synthesis 

 of trimethylamine oxide has been worked out for the fish or for any other 

 living organism. Baldwin (I95I) suggested that trimethylamine oxide may 

 be endogenous in origin, since some marine teleosts cein excrete up to 30 



Ik 



