The Preparation of Colorimetric Standards

In colorimetric determinations it is often found when the color is developed that the standard and unknown differ too much for accurate readings. Usually this is remedied by beginning the determination again and using a different amount of standard or unknown sample. It would be quicker to increase the color by the addition of more standard directly to the paler of the two colored solutions, if it were known that the increase in color intensity were proportional to the amount of added standard. The present investigation established the proportionality between increased color and additional standard added after color has been developed according to the usual procedure, as follows: for the determination of phosphate (Fiske and Subbarow), with an error of less than 2%; of creatinine (Folin), with an error of less than 1%; and of ammonia (preformed or from digestion of nitrogenous material) by nesslerization (Koch and McMeekin) within 5%. Uric acid added after the other reagents in the Christman and Ravwich modification of the method of Benedict and Franke, produces no color, hence the colored solution cannot be fortified in this determination

The Role of Oxygen Tension in Penile Erection and Its Relationship to Erectile Dysfunction

The corpus cavernosum of the penis is one of the few vascular beds in which there is a change in oxygen tension with function (blood PO2 25-40mm Hg in the flaccid state, and 90-100mm Hg in the erect state). This change in oxygen tension exposes the components of the corpus cavernosum to a variety of cytokines, humoral, vasoactive, and growth factors which may affect the structure and function of the endothelial cells, smooth muscle cells, neurons and extracellular matrix. Among these cell types, endothelial cells are the first line of defense to blood-borne stress and can affect the underlying smooth muscle via paracrine mechanisms. Impotence is defined as the inability to obtain or sustain an erection sufficient for vaginal penetration and can result from a variety of pathological conditions, vascular disease, endocrine disease, neurological disease, and psychogenic disorders. The penis is a vascular organ and as such is susceptible to the effects of vascular diseases. This review will discuss the basic etiology of erection and vasculogenic erectile dysfunction and explore the role oxygen tension in regulating various cellular and humoral factors as well as trabecular structure and function

Break junctions of the heavy-fermion superconductors

Mechanical-controllable break junctions of the heavy-fermion superconductors can show Josephson-like superconducting anomalies. But a systematic study on the contact size demonstrates that these anomalies are mainly due to Maxwell's resistance being suppressed in the superconducting heavy-fermion phase. Up to day, we could not find any superconducting features by vacuum-tunnelling spectroscopy, providing further evidence for the pair-breaking effect of the heavy-fermion interfaces.Comment: 5 pages, EPS figures included, REVTeX, to be published in Physica B 9