The total number of airborne micro-organisms collected on Nuclepore filters was determined by acridine orange staining and epifluorescence microscopy. The viable fraction of the total numbers varied significantly when actinomycete and fungal spores from different environments were stored on the filter surface for 1 week, although the microflora composition was not altered. A high correlation between viable and total counts was noted in environments where the airborne flora was dominated by fungal spores, while a low correlation was found for airborne bacteria. Peak values of the total counts registered in some work environments varied between 10(7) and 10(11) micro-organisms/m3. Size analysis showed a dominating fraction of respirable micro-organisms (aerodynamical diameter less than 5 micron). The investigation shows that it is of the utmost importance to combine viable counts with total count enumeration in the study of exposure to micro-organisms in work-related situations.

As a part of a worldwide investigation on the prevalence of respiratory symptoms, we have performed a study on the relationship between the indoor environment and asthma-like symptoms in the population of a central Swedish municipality. The study comprised 88 individuals, aged 20-45 years who underwent a structured interview, spirometry, a methacholine provocation test, skin-prick tests and blood samples for measurements of serum concentrations of eosinophil cationic protein (S-ECP), blood eosinophil count and total immunoglobulin E (S-IgE). In the homes, the room temperature, air humidity, respirable dust, house dust mites (HDM) and airborne micro-organisms were measured. The relative humidity in all the homes was found to be above 33%. HDM were found in 13% of homes. In the homes of the 47 subjects with asthma related symptoms, significantly higher total levels of bacteria and mould (P < 0.05) and a higher proportion of detected HDM (OR = 5.3) was found than in subjects with no asthma related symptoms, after adjustment for age, sex, smoking, indoor temperature and air humidity. HDM were found to be an independent risk factor for asthma related symptoms (OR = 7.9) and nocturnal breathlessness (OR = 6.2) (P < 0.05), while the total level of bacteria was a risk factor for asthma related symptoms and wheezing (P < 0.05). We conclude that although HDM is relatively infrequently found in the homes of central-Sweden, the presence of HDM is related to asthmatic symptoms. A relation between levels of airborne bacteria and asthma related symptoms was also found.

The discharge of impulses from the muscle spindle of the frog, when subjected to a constant mechanical stimulus (stretch), may show great irregularity. This is most noticeable when the muscle is near its resting length. The mean rate of impulses is then very low, and successive intervals appear to vary in a random manner. As the muscle is stretched, the rate of afferent discharge increases and irregularities become less obvious (Matthews, 1931).A possible explanation of the random discharge at low frequency has been suggested by Katz (1950a, b), on the basis of observations on single sensory nerve endings. Depolarization of the terminal branches of an axon in a muscle spindle was found to be responsible for the initiation of sensory impulses, the rate of the discharges depending upon the intensity of the local potential change. Fluctuations of the level of depolarization would therefore cause irregularity of the intervals between successive impulses. Such fluctuations of potential might be due directly to thermal agitation of ions in the nerve terminals, or they might be produced indirectly by molecular agitation in the mechanical receptor substance.At present, little is known about the mechanical receptor system, but the effects of thermal agitation in nerve endings can be subjected to a tentative theoretical analysis (see Fatt & Katz, 1952). Thus, the finer the diameter of a fibre, the larger will be the amplitude of 'voltage noise' at the terminal.For example, for an extremely fine ending, 0-1 ,u in diameter, a voltage fluctuation of the order of 0 5 mV r.m.s. has been estimated. The present experiments were planned to investigate whether this simple source of physical random disturbance could explain the observed fluctuations of impulse discharge. The irregularity was measured over a large range of frequencies of firing, applying various amounts of stretch to the muscle. * With a scholarship from the Swedish Medical Research Council.

Summary. A slight modification of Barker and Summerson's method of lactic acid determination is described. The rates of lactate utilization, urinary lactate excretion and blood glycolysis during recovery from prolonged muscular exercise were studied in two subjects working on a bicycle ergometer. The results indicate that under the specified conditions  the rate of lactate utilization is not significantly altered by anoxia caused by inhalation of low percentage oxygen mixtures.  the rate of blood glycolysis is low compared with the utilization rate of lactate and is independent of the blood lactate level.  the rate of urinary lactate excretion is very low compared with the utilization rate of lactate. and is independent of anoxia. The difficulties in determining the chemical order of the lactate utilization processes are discussed.

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