OYSTER CULTURE EXPERIMENTS IN LOUISIANA. 45 



relief, heavily charged though it may be with suspended mineral 

 particles and salts in solution. 



More common phenomena of the oyster beds are the seasonal and 

 irregularly periodical fluctuations in the condition of the oysters. In 

 some years the oysters in certain regions may be fat and in other 

 places i^oor, Avhile at another time the conditions will be wholly 

 reversed. Again seasons will occur when the oysters are poor almost 

 everywhere without apparent reasons. That these fluctuations are 

 immediately due to the relative abundance or scarcity of available 

 food admits of but little doubt, but granting that the assumption be 

 true the difficulty instead of being solved is merely shifted to a more 

 remote cause. Is there an actual deficiency in the quantity of food 

 organisms and if so, what are the chemical, physical, and biological 

 causes producing it? Or is there an abundance of food merely un- 

 available on account of some peculiarity of its distribution? 



The feeding of oysters has been studied for many years, both in 

 this country and in Europe, but we still know very little concerning 

 the subject, other than the mere nature of the food and the general 

 anatomical means by which it is ingested. It is only within three 

 years that it has been possible even approximately to estimate the 

 comparative volumes of the food carried b}^ the waters of different 

 localities, and such data are available for but a few places, all 

 previous results being too indefinite to be of any material value. 

 Even with the methods at present employed the results are not justly 

 comparable between various localities unless large numbers of obser- 

 vations are made embracing all average weather conditions; though 

 in the case of neighboring localities, where the Aveather conditions 

 may be assumed to be approximately the same, simultaneous or 

 approximately simultaneous observations may be accepted as com- 

 parable. 



It may be observed in the preceding tables, presented in the dis- 

 cussion of the experiments in oyster culture, that there is wide diver- 

 gence in the number and volume of the food organisms present in the 

 water at dift'erent times. In Pelican Lake, for instance, the number 

 of diatoms and other food organisms varied between 1,800 and 36,000, 

 while their volume ranged between 0.077 and 0.943 cubic millimeter 

 per liter of water (a cubic millimeter is about equal to the volume 

 of a cube measuring one twenty-fifth of an inch in diameter, arid a 

 liter is about 1^ quarts). This divergence is due very largely to 

 the varying state of the weather, the smaller results being as a rule 

 obtained after and during periods of calm, while the higher ones 

 were invariably observed at times when strong winds prevailed. The 

 reason for this is readily understood. The water specimens for 

 the determination of the food content are taken from the stratum 

 lying between 2 and 12 inches of the bottom. Many of the or- 



