A rapid naphthol yellows method for measuring the cellular protein content of anchorage cultures

Summary A rapid method has been developed for measuring the cellular protein content of mono- and multilayered anchorage cultures. Fixed or air dried cultures are stained for 30 min with 0.2% Naphthol Yellow S (NYS) dissolved in 1% acetic acid. Unbound dye is removed by a series of four 2.5 min washes in 1% acetic acid, and protein-bound dye extracted with 10 mM unbuffered Tris base for spectrophotometric optical density determination at 433 nm. The NYS method exhibited a least-squares correlation coefficient of 0.99997 with the Oyama-Eagle Lowry method.     

Nonvisual feeding in a visual planktivore,Xenomelaniris venezuelae

Summary Studies of the diel feeding patterns of the planktivorous fish, Xenomelaniris venezuelae, in Lake Valencia, Venezuela, revealed that, although the fish is primarily a diurnal feeder, it consumes substantial numbers of Chaoborus larvae and pupae at night. A number of fish species are known which feed on plankton at night, but these fish are filter feeders and their diets largely consist of relatively small, nonevasive prey. Chaoborus, however, is large and agile. Predation by Xenomelaniris in the dark was also studied experimentally. Captured fish were placed in completely darkened aquaria with zooplankton from Lake Valencia. After several hours the plankton was removed and examined for evidence of feeding. The fish were found to consume Chaoborus pupae and fourth instar larvae but not other types of prey. The mode of feeding by Xenomelaniris in the dark is unknown.     

An age dependent stochastic model of periodic screening: Basic properties

An age dependent stochastic model for the periodic screening of a progressive chronic disease is developed in this paper by combining results from previous modeling efforts. The basic concepts used are the random variables describing the disease free state and preclinical state sojourn times and the age at screening or observation, as well as generations of individuals defined according to time of entry into the preclinical state. At discrete time points, the model characterizes the density functions for individuals who are healthy, have preclinical disease, or have clinical disease. The joint density functions of age and sojourn times for cases detected by a periodic screening program and for cases which surface clinically between screens are derived as functions of screening interval, false negative rate, and disease natural history.     

CHANGES IN HEPATIC STRUCTURE IN RATS PRODUCED BY BREATHING PURE OXYGEN

The livers of rats exposed to pure oxygen were examined electron microscopically to study toxic effects of oxygen in a metabolically sensitive organ. Pressures of 1/3 (258 mm Hg), 1 (760 mm Hg), and 3 (2280 mm Hg) atmospheres were used, with exposures up to 90 days with the lowest pressures. The first changes in the hepatocytes were loss of glycogen and enlargement of mitochondria with development of mitochondria with bizarre shapes which were seen after 3 days at 258 mm, 1 day at 760 mm, and 3 hours at 2280 mm. These changes were followed by formation of increased numbers of cristae, membranes surrounding mitochondria, autophagic vacuoles, and polyribosome clusters. After 2 weeks at 258 mm, which is the pressure of the atmosphere of space cabins, numerous mitochondrial myelin figures appeared but the mitochondrial enlargement had begun to regress. After 90 days at 258 mm, the liver cells appeared almost normal except that many pigment granules had accumulated in the pericanalicular zones. The changes were non-specific and seemed to parallel biochemical alterations recorded elsewhere. They are not considered the result of toxicity but rather of adaptation. These atmospheres, which are used in clinical medicine and in space travel, appear to have no permanent deleterious effects on the liver in rats under the conditions of this experiment.