Laboratory study of Mycobacterium bovis infection in badgers and calves.

Two experiments with badgers infected with Mycobacterium bovis are described. In the first, badgers were infected by intravenous inoculation of a bovine isolate of M bovis. The course of the disease in these and its spread to healthy badgers and calves was monitored by clinical, immunological and bacteriological means. In the second experiment a group of naturally infected badgers were observed for a period of up to four years. They were found to excrete M bovis in their faeces for periods of between 165 and 1305 days before they died of tuberculosis or were killed. M bovis was also shed in the urine. The badgers in both experiments were examined regularly and blood samples were taken for complement fixation tests. Faeces, urine, pus and sputum were also collected for cultural and biological tests and the badgers were skin tested using Weybridge bovine and avian tuberculin. The skin tests were uniformly negative while the complement fixation test were positive in some infected badgers but gave very variable results. Only the isolation of M bovis gave a definite diagnosis of tuberculosis in the living badger but a number of badgers which were found to have tuberculosis at post mortem were not detected while alive by this method. Environmental samples from the yards, including badger faeces, soil, hay, scrapings from feeding bowls and water were regularly examined for the presence of M bovis but apart from faeces only one water sample was positive, indicating that the organism did not persist for long in the environment. In both experiments calves developed sensitivity to bovine tuberculin after six months' exposure to infected badgers. The experiments further demonstrate the potential of a badger population to become endemically infected with M bovis and to act as a source of infection for cattle.

Diffusion of oxygen through the mouse ear.

Oxygen tension differences across the mouse ear have been measured polarographically under conditions of no blood flow. For some experiments the ear was split into two by cleavage along the central cartilage plate, and the diffusion of oxygen measured in both directions across these asymmetrical preparations. Measurements were also made on ears from which the stratum corneum had been removed by stripping with Sellotape. It was possible to relate these results to a simple multi-layer diffusion model. The main barrier to diffusion of oxygen resides in the stratum corneum, whose permeability is estimated to be 1 . 2 X 10(-8) ml O2 atm-1 cm-1 S-1. The permeability of the rest of the ear is 4 . 7 X 10(-7) ml O2 atm-1 cm-1 S-1. The inhibition of tissue respiration by the local injection of solutions of sodium amytal, potassium cyanide and other substances reduced the oxygen gradients by factors of between 3 and 7. Cooling the ear from room temperature to 0 degree C reduced the gradients by a factor of about 4.

The diffusion coefficient of oxygen in respiring kidney and tumour tissue.

The diffusion coefficient and permeability, together with the oxygen uptake rate, have been measured in slices of respiring tissue. Values of these quantities are given for mouse kidney cortex and for implanted tumours of Lewis lung carcinoma in the mouse, and the fibrosarcoma SSB1a in the rat. The diffusion coefficient at 22 degrees C is 1.3 . 10(-5) . cm2 . s(-1) in the kidney, and has the higher value of 1.6 . 10(-5) . cm2 . s(-1) in both tumours. The solubility in all three tissues is similar to that in saline.

The spatial correlation of fluctuations of the blood flow in forearm skin.

The oxygen tension at the skin surface, with the atmospheric oxygen supply excluded, may be measured polarographically on the human forearm. Under suitable environmental conditions, spontaneous fluctuations in skin surface oxygen tension can be recorded and these are the result of fluctuating blood flow in the superficial skin vessels. An array of separate cathodes in a single polarographic electrode assembly has been used to measure the fluctuations in blood flow which are occurring simultaneously at seven different points in the skin. Spectral analysis of a long recording of such fluctuations shows that most of the power is concentrated at the lower frequencies but does not reveal any clearly defined dominant frequency. It is clear, however, from inspection of the fluctuation patterns, that recurring bursts of activity occur with quite well-defined periodicities in the range of 30s to 5 min. There is a stronger correlation between the fluctuations occurring at points on the skin surface less than 1 mm apart than between points further apart, although there are clearly some components which are common to points separated by up to 5 mm which was the largest separation of cathodes used in these experiments. These observations are supported by the value of cross correlation coefficients between the channels. These results suggest that the observed fluctuations are the result of at least two factors. The first one is common to all the channels but the effect of this may be overridden by a second and more local one controlling the blood flow.

A simple method for isolating leucocytes from bovine blood and their separation into lymphocyte and granulocyte fractions.

A method for the separation of leucocytes from bovine blood and its separation into lymphocyte and granulocyte fractions is described. The method, involving flash lysis of the erythrocyte population, was found to yield large numbers of viable cells suitable for maintenance in tissue culture medium and hence of value in immunological studies.