Mixed Venous and Arterial Pco2

The rebreathing method of measuring oxygenated mixed venous Pco₂ (P$\bar{v}$co₂) was originally introduced as a bloodless way to estimate arterial Pco₂ (Paco₂). It has become common practice to subtract 6 mm Hg from the P$\bar{v}$co₂ to obtain the Paco₂ but there are many circumstances in which this leads to an overestimate of the Paco₂. Measurements of P$\bar{v}$co₂ and Paco₂ in 19 patients have shown that a better approximation to Paco₂ under normal conditions of cardiac output and arterial O₂ saturation is Paco₂ = 0·8 P$\bar{v}$co₂. These studies also showed that the P$\bar{v}$co₂ — Paco₂ difference may be much wider, particularly in the presence of arterial unsaturation and a low cardiac output.The factors governing the venoarterial Pco₂ difference are reviewed and their magnitude is calculated to emphasize the complementary roles of measurements of P$\bar{v}$co₂ and Paco₂ in the assessment of patients with cardiorespiratory disease.     

Miliary tuberculosis in British Columbia

The case records were studied of all 48 patients with miliary tuberculosis registered by the British Columbia Division of Tuberculosis Control between 1967 and 1971. Two groups of patients were found, one group of 30 in whom the diagnosis was made during life and antituberculous therapy instituted, and a second group of 18 patients in whom the diagnosis was made only at autopsy and who had received no antituberculous therapy. In the latter group there was a particularly high incidence of concomitant disease; additionally, tuberculin testing, bacteriological search for acid-fast bacilli and chest radiography were frequently neglected. This group consisted mainly of elderly male Caucasians. The disease was characteristically insidious in onset, frequently with non-specific symptoms and physical findings. Fever was a common presenting symptom. Several patients presented with a fulminant illness which, although diagnosed, was not affected by antituberculous therapy and was rapidly fatal. North American Indians showed a high incidence of disease but a low mortality rate, probably owing to their younger age.     

Homology of Ribosomal Ribonucleic Acid of Desulfovibrio Species with Desulfovibrio vulgaris

Three species of Desulfovibrio were found to have a high degree of ribosomal ribonucleic acid homology with Desulfovibrio vulgaris. Desulfotomaculum nigrificans, which is also a sulfate-reducing anaerobe, had only 38% ribosomal ribonucleic acid homology with D. vulgaris. The homologies of six other unrelated genera were determined and found to be lower than 50%.     

Contribution of organic carbon and clay to cation exchange capacity in a chronosequence of sandy soils

Summary CEC and oxidisable carbon content were highly correlated (r=0.96) whereas a lower coefficient was obtained for a correlation of CEC and clay content (r=0.57) in a chronosequence of sandy soils from New Zealand. Partial regression coefficients for oxidisable carbon were highly significant in multiple regression equations for all soil groupings whereas in only one equation was the coefficient for clay significant. The CEC of the organic matter for all soils was 1.4 me/g and this value decreased from 1.64 me/g in the young soils to 1.22 me/g in old soils. Peroxidation of selected surface samples caused a reduction in CEC but the results indicated that the clay fractions had a considerably higher CEC (0.57 me/g) than that inferred from multiple regression equations for untreated samples. Selective dissolution analysis indicated that the clay fractions of these soils contained an appreciable amount of amorphous material. Reduction in the CEC of the clay fraction apparently occurs through a blocking by organic matter of the negative charge of the clay components.