was confirmed by Yonge (1926a) and Graham 

 (1931a, 1931b). The enzymes were obtained by 

 grinding the styles with sand and extracting for 

 2 to 3 days in distilled water with a small amount 

 of toluol as an antiseptic. For testing, the 

 5-ml. samples of 1 percent extract of style were 

 treated with 2 ml. of hydrogen peroxide and 12 

 drops of 1 percent pyrogallol. After 5 minutes 

 the sample turned dark red-brown. The ex- 

 tract produced color even in the absence of hydro- 

 gen peroxide, indicating the presence of a complete 

 oxidase system. Reactions with guaiacum and 

 2 percent hydroquinine were less pronounced 

 than with pyrogallol. 



Sawano (1929) reported the presence of buty- 

 rase, an enzyme that clots milk, in the styles of 

 0. circumpicta but his observation remains un- 

 confu-med. 



Extracts of digestive diverticula contain a 

 large array of sucroclastic enzymes which act 

 on starch, glycogen, sucrose, maltose, lactose, 

 rafRnose, and on some glucosides. The amylase, 

 which converts starch into dextrin and dextrin 

 into maltose, is present both in the style and in 

 the digestive diverticula of the oyster. It has, 

 however, different optima; the style amylase 

 acts best at pH 6.0, whereas the enzyme from 

 the diverticula has an optimum at pH 6.4 (Sawano. 

 1929). 



The proteolytic enzyme of 0. edulis is absent 

 in the gut but can be found in the extract of the 

 diverticula. It acts very slowly and has two pH 

 optima at 3.7 and 8.5 when casein is used as a 

 substrate. With gelatin the optima are 4.1 and 

 8.5. 



Cellulase, the enzyme which hydrolizes cellulose, 

 has not been found in the digestive extracts of the 

 oyster. It must be assumed, therefore, that the 

 oysters are unable to digest cellulose. The 

 possibility is not excluded, however, that this 

 enzyme may be present in the bacteria and fungi 

 which happen to be in the gut. The presence 

 of cellulase in mollusks has been established for 

 the gastropods Helix and Linnaea and for the wood 

 boring bivalve Teredo. 



Fats are hydrolized to fatty acids and alcohols 

 by the action of lipase. Yonge (1926a) dem- 

 onstrated the presence of this enzyme by 

 feeding the oysters an emulsion of olive oil stained 

 red with Nile blue sulphate and watching the 

 change of red color into blue as the digestion 

 proceeded. Oil is ingested by phagocytes and is 



carried by them through the tissues, the gradual 

 change of color serving as an index of the action 

 of lipase. From the observation that the droplets 

 of oil found free in the stomach retain the red 

 color, Yonge deduced that free lipase is absent 

 in the gastric juice. These findings are contra- 

 dicted by the observations of George (1952) who 

 showed that in C. virginica and in Mytilus the 

 hydrolysis of neutral fats takes place extra- 

 cellularly in the stomachs and that lipase can be 

 extracted from the crystalline style. According to 

 his observations, droplets of olive or peanut oil 

 stained scarlet red with Sudan I or Sudan III 

 are not deposited in the tissues. It is known 

 that in mammals and birds the stained fat may 

 be stored in the bodies (Gage and Fish, 1924). 

 Several possibilities may be considered: (a) that 

 the stained fat is rapidly metabolized; (b) that 

 it may be deposited in connective tissue in minute 

 quantities undetectable under the light microscope; 

 and (c) that the mollusks are unable to utilize 

 the peanut and olive oil because of the differences 

 between the fatty acids of these oils and the 

 unsaturated fatty acid of their natural food. So 

 far no experimental evidence has been presented 

 in support of any of these possibilities (George, 

 1952) and further studies of the problem of fat 

 digestion in bivalves are needed. 



pH CONTENT OF GUT AND STOMACH 



The digestive fluids found in the alimentary 

 tract are acid. The most acid conditions exist in 

 the stomach (average pH 5.5) due to the dis- 

 solution of the crystalline style, which has a pH 

 of 5.2 (5.4 in starved animals), and, according 

 to Yonge {1926a), is the most acid substance in tho 

 gut. In the absence of the style the pH of thfl 

 stomach fluids increases. This has been demon- 

 strated on oysters with clamped shells, kept for 6 

 days out of water. Under these conditions the 

 pH of the stomach rose from 5.67 to 6.14 while the 

 pH of the liquid in the mantle cavity decreased 

 due to the accumulation of carbon dioxide from 

 6.7 to 6.14. It is significant that the acidity in 

 the stomach caused by the dissolution of the style 

 approximates the optimum (pH 5.9) for the action 

 of the style's amylase. The pattern of pH dif- 

 ferences in various parts of the alimentary tracts 

 as shown by Yonge is as follows: esophagus 5.6- 

 6.0; stomach 5.4-5.6; style 5.2; midgut 5.5-6.0; 

 rectum 5.8-6.3. The pH of the extracts of the 

 styles of C. virginica, determined by placing the 



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FISH AND WILDLIFE SERVICE 



