Some observations on air filtration

Summary 1. A method has been developed for testing the filtration efficiency of some filter materials. For each of the materials investigated — cotton wool, stillite and carbon — a suitable filter has been devised.2. The filtered air was analyzed as to its germ content with the aid of a set of 3 capillary impingers.3. The cotton wool filter gave on the whole satisfactory results provided that due attention was given to the packing of the filter and its sterilisation. Clear indications were obtained that the degree of the contamination of the air was of vital importance.4. The stillite filter proved to have the advantage of combining a high filtration efficiency with a low resistance to the passing air. Also for the stillite filter a critical degree of contamination of the air was established; on surpassing this degree the filtration effect was endangered.5. The carbon filter proved to be most efficient, but had a relatively low specific filtering capacity. It was found that the filtration result was depending on the height of the carbon column and on the velocity and the degree of contamination of the air.6. It should be stressed that in all experiments artificially contaminated air was used, and that the number of germs present in the air to be filtered was in all cases many times larger than that usually occurring in normal air.     

Some observations on glass-knife making

The yield of usable knife edge per knife (for thin sectioning) was markedly increased when glass knives were made at an included angle of 55 degrees rather than the customary 45 degrees. A large number of measurements of edge check marks made with a routine light scattering method as well as observations made on a smaller number of test sections with the electron microscope indicated the superiority of 55 degrees knives. Knives were made with both taped pliers and an LKB Knifemaker. Knives were graded by methods easily applied in any biological electron microscope laboratory. Depending on the mode of fracture, the yield of knives having more than 33% of their edges free of check marks was 30 to 100 times greater at 55 degrees than 45 degrees.     

Some morphological observations on osteoclasts

Summary Osteoclasts of the peripheral portions of the endocranial aspect of young rat parietal and frontal bones were studied by scanning electron microscopy of glutaraldehyde fixed, critical point dried specimens. These studies show Osteoclasts to have a much more complicated form than has previously been realised. Extensively branching, elongated, smooth-surfaced cells, which are for the most part elevated above the level of the surrounding bone matrix surface and sometimes above portions of osteoblasts or other osteoclasts, were identified as motile non-resorbing cells. Portions of the former and other entire cells may be embowered in Howship's lacunae, have microvilli on their dorsal surface, and are surrounded by a serrated border of microprojections which have an apparently firm attachment to the matrix surface. Osteoclasts in short term culture show additional free surface ruffles which are not encountered in specimens taken fresh from the animal. No evidence of recruitment of osteoblasts or osteocytes into osteoclasts was found. Disinterred osteocytes retained an ability to migrate from their lacunae on to surrounding bone matrix surface.We would like to thank Elaine Maconnachie for expert technical assistance and Dr. Martin J. Evans for the use of his tissue culture laboratory. These studies have been supported in part by a grant from the Medical Research Council     

Pathogenesis of viral hepatitis

The aim of our research is to use animal models to elucidate the molecular basis for viral clearance and liver disease in the pathogenesis of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections. The results herein discussed provide insight into immunological and virological processes that may lead to the development of new therapeutic strategies to terminate chronic HBV and HCV infections.     

Some ecological observations on floating islands

The paper reports the occurrence of floating islands in an impoundment infested with water hyacinth. Data on chemical composition of the islands, the surrounding water and the bottom soil of the impoundment are given, to show that the floating islands are rich reserves of nutrients and differ considerably from their surroundings. Some comments have also been made on their development and their importance in water resource management.     

Some recent observations on Orkney Sheep

This Paper describes the semi-feral sheep of North Ronaldsay. These sheep are of the Orkney breed, and feed almost entirely on seaweed. Hitherto unpublished material on the numbers of these sheep and on certain biochemical polymorphisms is presented.