Sudden Failure of Swimming in Cold Water

To investigate the effect of cold water on swimming four men who declared themselves good swimmers were immersed fully clothed on separate days in water at 23·7° and 4·7° C. The time that they were able to swim in the cold water was much shorter than in the warm. The two shortest swims ended after 1·5 and 7·6 minutes, before rectal temperature fell, when the men suddenly floundered after developing respiratory distress with breathing rates of 56–60/min. The other cold swims, by the two fattest men, ended less abruptly with signs of general and peripheral hypothermia.It is concluded that swimming in cold water was stopped partly by respiratory reflexes in the thin men and hypothermia in the fat, and partly by the cold water''s high viscosity. The longer swimming times of the fat men are attributed largely to their greater buoyancy enabling them to keep their heads above water during the early hyperventilation.The findings explain some reports of sudden death in cold water. It is clearly highly dangerous to attempt to swim short distances to shore without a life-jacket in water near 0° C.     

On the site of action of phosphatide acyl-hydrolase activity of rat brain homogenates on lecithin

The hydrolysis of 2- [14C]acyl-labelled and [Me-3H]choline-labelled lecithins by rat brain homogenates has been studied. The acyl-labelled substrate was hydrolysed with the production of both radioactive lysolecithin and radioactive free fatty acid in the proportions of 60 per cent and 40 per cent; traces of labelled mono- and diglyceride were also formed. In addition to radioactive lysolecithin the [3H]choline-labelled lecithin also gave rise to much smaller amounts of radioactive water soluble derivatives, consisting almost entirely of free choline and phosphorylcholine with only traces of glycerylphosphorylcholine. The results provide evidence for the production of a mixture of 1- and 2-acyl isomers of lysolecithin by phospholipase action in brain homogenates at pH 7.4, the latter predominating slightly.     

Identification of Fluorescent-Antibody Labeled Group A Streptococci by Fluorometry

A quantitative system, amenable to automation, for determining the presence of group A streptococci in broth culture is described. After separation from the broth, the cells' protein coats are removed by digestion with 0.1% trypsin, and they are then stained with anti-A fluorescent antibody (FA). Excess FA is removed, and bound FA is put into solution by dissociation with demineralized distilled water. The amount of FA bound to the cells is quantitated by fluorometry of the solution. The level of nonspecific staining is measured by staining the cells with fluorescein-conjugated normal rabbit globulin absorbed with group A cells, dissociating, and quantifying, as above. The two quantities are subtracted to measure specific binding of FA to group A cells. A clinical trial showed 92% agreement with microscopists.     

Oxygen cost and oxygen uptake dynamics and recovery with 1 min of exercise in children and adults.

To test the hypothesis that O2 uptake (VO2) dynamics are different in adults and children, we examined the response to and recovery from short bursts of exercise in 10 children (7-11 yr) and 13 adults (26-42 yr). Each subject performed 1 min of cycle ergometer exercise at 50% of the anaerobic threshold (AT), 80% AT, and 50% of the difference between the AT and the maximal O2 uptake (VO2max) and 100 and 125% VO2max. Gas exchange was measured breath by breath. The cumulative O2 cost [the integral of VO2 (over baseline) through exercise and 10 min of recovery (ml O2/J)] was independent of work intensity in both children and adults. In above-AT exercise, O2 cost was significantly higher in children [0.25 +/- 0.05 (SD) ml/J] than in adults (0.18 +/- 0.02 ml/J, P less than 0.01). Recovery dynamics of VO2 in above-AT exercise [measured as the time constant (tau VO2) of the best-fit single exponential] were independent of work intensity in children and adults. Recovery tau VO2 was the same in both groups except at 125% VO2max, where tau VO2 was significantly smaller in children (35.5 +/- 5.9 s) than in adults (46.3 +/- 4 s, P less than 0.001). VO2 responses (i.e., time course, kinetics) to short bursts of exercise are, surprisingly, largely independent of work rate (power output) in both adults and children. In children, certain features of the VO2 response to high-intensity exercise are, to a small but significant degree, different from those in adults, indicating an underlying process of physiological maturation.     

Amoeboid locomotion of Naegleria gruberi: the effects of cytochalasin B on cell-substratum interactions and motile behavior

The major manifestations of amoeboid locomotion in Naegleria-cytoplasmic streaming, pseudopod production, cell polarity and focal contact production-require that the actin-based cytoskeleton be extremely dynamic. Whether these features are causally linked is unclear. In an attempt to answer this question we have used the fungal product cytochalasin B (cyt B) to dissect the motility process. This drug can perturb the organisation of actin filaments both in vivo and in vitro. Essentially cyt B acts as a molecule which can cap the barbed ends of actin filaments. Not surprisingly, therefore cyt B has an effect on rates of actin polymerization and the dynamic state of actin in the cytoplasm. We have found that cyt B has a profound effect on focal contact production and breakdown. Within minutes of addition of cyt B focal contact production ceases, existing focal contacts are stabilised but cytoplasmic streaming and pseudopod production are not blocked. In conclusion it is now clear that the state of actin required for focal contact production is different from that required for pseudopod extension and cytoplasmic streaming.