fëeâe&nc6> Φηοφΐ€4ά Microsectioning
Method
A new method of slicing biological tissue in ultrafine .sections has been developed by S. B. Newman. Kmil Borysko, and Max Swerdlow of the National Bureau of Standards. The apparatus opens new fields of research to investi gators studying cell structure. The technique produces uniform s c iions of tissue a fraction of a micron in thickness for study with the electron microscope, utilized in such fields as cancer research and the study of virusdiseases. Since The electron beam in commercial instruments has slight pene trating power compared to the depth of the field involved, extremely thin sections are necessary and were heretofore difficult and expensive to obtain. In the new procedure η-butyl methacrylate is polymerized around the speci men to produce an optically clear em bedding medium with good cutting prop erties. A slightly modified microtome is then used, the unique feature of which is the method of smooth, continuous ad vance of the specimen toward the knife. The specimen holder is a metal which is made to expand thermally. I t is es sentially a brass block containing a hole threaded at one end to receive a stand ard %-in. brass pipe plug. A cavity in the face of the plug provides a seat for the embedded specimen. Behind the plug is a needle valve, which admits compressed carbon dioxide gas to the interior of the block. As the gas in creases in volume, it cools and contracts the assembly. Reducing Cut sections the gas flow allows the apparatus to approach room temperature, and thus the thermal expan sion allows continuous advance of the embedded tissue toward the cutting edge. Initial preparation of the specimen involves de hydration in an ethyl al cohol series and transfer to a solution containing equal parts of absolute a l c o h o l and n-butyl methacrylate. After an hour in the mixture the tissue is placed in the monomer alone, repeat edly to ensure removal of the alcohol. Gelatine capsules are the embed ding molds. They con tain the monomer plus 1% by weight of 2,4dichlorobenzoyl peroxide 2014
as polymerization catalyst. After 6 to 8 hours of heating at 45-50° C . the mono mer is polymerized into a solid matrix containing the tissue embedded at the bottom, and the capsule is removed by soaking in water.
First Clinical Findings Neomycin Reported
on
First clinical findings on the thera peutic use of neomycin indicate potential value for the new antibiotic in the treat ment of tuberculosis and certain acute infections. Neomycin was first isolated by Selman A. Waksman of Rutgers University who also first isolated strep tomycin. Work done independently by Geoffrey Rake of the Squibb Institute for Medical Research and Gladys L. Hobby and her associates at the biologi cal laboratory of Chas. Pfizer & Co., Inc., was reported at the recent con ference on "The Chemotherapy of Tu berculosis—The Experimental Approach" sponsored by the New York Academy of Sciences. Dr. Rake reported that against murine tuberculosis neomycin was effective when applied subcutaneously in dosages ap proximately twice as large as those used for streptomycin. Given orally, neomy cin showed no apparent effect in doses up to 175,000 units. He estimates the toxic dose of neomycin as 15 times the therapeutic dose whereas that of strep tomycin is in the ratio of 300 to 1. Dr. Rake found neomycin to be effec tive against organisms causing acute inare lifted with camel's hair brush
fections. Against salmonella, an organ ism causing a form of dysentery, cures were obtained with 67 units of neomycin given subcutaneously or with 390 units given orally. Results of tests carried out by Dr. Hobby and her associates at Pfizer, Tulita F. Lenert and Nancy Dougherty, indicate that neomycin is capable of exerting an antimicrobial effect against both Gram-positive and Gram-negative microorganisms, as well as against strep tomycin-sensitive and streptomycin-re sistant strains of murine tuberculosis. The frequency with which organisms resistant to the action of streptomycin emerge during therapy is one of the major drawbacks to the use of strepto mycin in the treatment of tuberculosis. Dr. Hobby also reported that studies in lower animals indicate that neomycin probably possesses a low degree of tox icity. It was found to be effective in pro tecting animals against infections due to organisms such as K. pneumoniae, E. typhosa, and Proteus vulgaris. Fur thermore, their preliminary studies indi cate that it is capable of supressing ex perimental tuberculosis infections in mice.
Plastics
in
Aircraft
"Plastics Inspection," an illustrated manual dealing with the nature of plas tics materials, their methods of fabrica tion, properties, and tests, is now avail able from the Office of Technical Serv ices. It includes a timetable on the development of commercial plastics, flow charts for the production of the more common types, and diagrams and photo graphs of test specimens and apparatus. Principal sections cover applications in aircraft and aeronautical equipment, terminology, molding and fabrication of thermosetting and thermoplastic plastics, and inspection, testing, and properties. An appendix deals with the raw mate rials and processes used in manufactur ing. About 150 photographs, drawings, and charts illustrate general principles and specific applications. PB 91836 may be obtained from the Office of Technical Services, Department of Commerce, Washington 25, D. C., at $2.75 per copy.
Scrub
Typhus
The application of chemicals such as dimethylphthlate and diethylphthlate to a person's clothes is an effective precau tion against the scrub typhus disease. This is the result of an investigation by an Indian zoologist, M. I. Roonwali, of the Zoological Survey of India. The results of his experiments, pub lished by the National Institute of Sci ence of India, show that the disease, which raged in a virulent form in the Assam jungles during World War II, is caused by the bite of tiny mites called trombiculids, which are found on the bodies of rats, screws, and monkeys. CHEMICAL
AND
ENGINEERING
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