Standard curves and reagent blanks are deter- 

 mined daily with double distilled water. The 

 reddish-violet reaction product is unstable. It is 

 easily destroyed by sunlight and oxidizing agents 

 with a resultant dark green coloration. In filter- 

 ing the sample it is necessary to establish that 

 passage through the filter does not introduce ex- 

 traneous carbohydrates. 



Collier, Ray, Magnitzky, and Bell (1953), ex- 

 pressed the results of their determinations in terms 

 of concentrations of arabinose (in mg./l.) although 

 the substance or substances present in the water 

 were not definitely identified. They state that 

 they "may not be true carbohydrates." 



A series of analyses using the N-ethyl-carbazole 

 method were made at Woods Hole of samples of 

 sea water pumped from the harbor to the labora- 

 tory. In July 195.3, the carbohydrate content was 

 low, varying from 0.3 to 1.8 mg./l. Many deter- 

 minations giving values of about 0.1 mg./l. were 

 almost below the threshold of sensitivity of the 

 method and many others had to be discarded be- 

 cause of contamination of the samples or deteriora- 

 tion of the reagent. 



A study of the records of shell movements and 

 water transport of oysters in relation to the natural 

 fluctuation of the carbohydrate content of sea 

 water in which they were kept gave negative re- 

 sults. No evidence was found to support the view 

 that the opening of the valves and the resumption 

 of water transport were associated with the in- 

 crease of carbohydrate concentration from 0.3 to 

 1.8 mg./l. The oysters opened and closed spon- 

 taneously regardless of the slight fluctuations in 

 the content of the substances which react with 

 carbazole. Several excerpts from the laboratory 

 records presented in table 20 illustrate this point. 

 Within the range of concentrations found in the 

 water, the high and low degrees of activity were 

 not correlated with the changes in the carbohy- 

 drate content (compare the behavior of oysters B, 

 B' and C, D'). In each case the recording was 

 continued for a period varying from 6 to 8 hours. 

 After periods of inactivity the oysters B', D, and 

 D' opened and resumed water transport, while 

 there was no change in the concentration of carbo- 

 hydrate. I deduce from these observations, which 

 were repeated several times with similar results, 

 that the presence of carbohydrates within the 

 range found naturally in Woods Hole sea water 

 had no effect on the oysters and is not a factor 

 which controls the function of their giUs. 



Table 20. — Carbohydrate concentration in sea water {mg./l.), 

 shell movements and water transport in C. virginica at 

 Woods Hole 



[Active shell movement means frequent opening and closing of the valves] 



The determinations of the concentration of 

 carbohydrates in Woods Hole water are in agree- 

 ment with the findings of Lewis and Rakestraw 

 (1955) for the Pacific Coast, where they encoun- 

 tered carbohydrates in quantities varying from 

 0.1 to 0.4 mg./l. and as high as 8 mg./l. in coastal 

 lagoons. 



If carbohydrates did in fact influence the rate of 

 water transport it would be reasonable to expect 

 that the addition of these substances in quantities 

 exceeding their concentration in natural water 

 would produce a measurable effect. Quantities 

 of various carbohydrates were added at a known 

 rate to the mixing chamber from which the water 

 was supplied to the constant level tanks with 

 oysters (Galtsoff and Arcisz, 1954). The fol- 

 lowing substances were used in concentrations 

 ranging from 10 to 100 mg./l.: arabinose, fructose, 

 dextrose, maltose, and ascorbic acid. The tests 

 were continued for several hours. In all cases 

 there was no evidence that the increase in carbo- 

 hydrate concentration in any way affected the 

 rate of water transport or shell movements of the 

 oysters. 



In some instances (first column, table 21) there 

 was a gradual increase in the activity of the gills 

 which cannot be attributed to the presence of 

 arabinose since the rate of water transport con- 

 tinued to increase for several hours after the return 

 of the oyster to natural sea water. 



Similar results were obtained in another set of 

 experiments using arabinose and fructose. The 

 following rates of transport of water were recorded: 



Before adding arabinose 



9.5 to 11.4 l./hr. during 2 hours 

 In arabinose solution (65 mg./l.) 



7.6 to 13.3 l./hr. during 4 hours 

 Return to natural sea water 



19.0 to 26.6 l./hr. during 3 hours 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



199 



