THE GENERAL FORM OF EXCRETION IN THE LOBSTER, HOMARUS

Abstract

1. A method is given for safely securing repeated evacuations of the nephridial bladders of the lobster, Homarus, thus permitting experimental analysis of nephridial function.2. Routine chemical analyses for blood, urine, and sea water are given.3. Experimental analysis shows that the nephridium can concentrate in the urine phenol red, para-aminohippurate, magnesium, and sulphate. At normal blood levels, it completely excludes glucose and Fiske-SubbaRow phosphate. Phlorizin blocks glucose retention. With high blood levels, the secretory or exclusion powers of the nephridium are swamped. Calcium is partially excluded from the urine. The nephridium is indifferent to inulin, bromsulfalein, dogfish hemoglobin and plasma protein, sodium and chloride. The ability of the digestive gland to concentrate phenol red and bromsulfalein in the digestive juice is noted.4. Exogenous urea is lost through the gills.5. The gills and carapace are relatively impermeable to magnesium and sulphate, and to phenol red, but are freely permeable to water, sodium chloride, and to exogenous urea.6. In full-strength sea water, the distribution of sodium chloride between sea water, blood, and urine seems to be passive. In dilute sea water, experiments indicate that blood chloride is elevated in some active fashion, presumably by the gills. The nephridium, however, does not aid in the conservation of chloride. Chloride is lost at the elevated blood level. The nephridium does not seem to have powers to deal actively with sodium chloride.7. The normal urine flow is approximately 1 ml./hr./0.5 kg., with wide variations. Water and sodium chloride for this flow enter largely through the gills although there may be intermittent contributions from the stomach. Magnesium and sulphate enter largely through the stomach. Calcium, in addition to that of sea water, is in the food. The lobster intermittently drinks sea water with food or on an empty stomach. The stomach contents are absorbed completely but not rapidly enough to furnish the fluid for the bulk of the urine flow. The daily urinary excretion of magnesium roughly equals the magnesium found in 5 ml. of sea water. All test substances entered the blood from the stomach. In any study of sea water and blood, the gastric contribution to the chemistry of the blood, even for electrolytes, must be considered.8. Lobsters from commercial pounds are frequently oliguric or completely anuric. Inability to form urine is not lethal, at least over a one-month period. Erratic transitory urine flows can be induced in anuric lobsters by the injection of various saline solutions. Normal urine flow can be induced in anuric lobsters by the transfusion of serum from one lobster to another. Apparently, substances such as blood proteins which are not diffusible through the gills draw in water which is bailed out by the nephridia. Osmolar measurements found the blood isotonic or slightly hypertonic, never isotonic, to sea water.9. While the nephridium has a range of capacities for dealing with individual substances (secretion, exclusion, partial exclusion, and a lack of partition power), its secretory capacities are not great and are masked easily by elevated blood levels. Nephridial removal of substances from the blood depends more on a flush-out principle, using large urine flows, than upon secretory powers. Some substances such as exogenous urea are lost by the gills and not by the nephridium. Together, the nephridia and the gills form an excretory system, each with individual capacities.