Search

The intrafusal fiber content observed in 850 spindles from seven kinds of limb muscles of the cat are presented. The tenuissimus had the smallest content, 6.14 fibers per spindle, and the extensor digitorum longus the largest, 7.91. Gastrocnemius spindles had more fibers than those in the soleus. The differences were attributable primarily to variation in number of nuclear chain fibers. No infallible correlation with anatomical or functional characteristics of the muscles was evident, although greater fiber content seemed to be associated with flexor action and fast contractility. The possible consequences of the spindle content of intrafusal fibers on static and dynamic sensitivity of its afferents are discussed in relation to available data on stretch sensitivity.

The incidence and patterns of association of tendon organs (TO's) with muscle spindles was studied in serial histological sections of the extensor digitorum brevis (EDB) muscles of an adult cat. Some observations were obtained from the medial gastrocnemius and soleus muscles of a second cat, and the EDB muscle of a two-toed sloth. An intimate relation of a TO to a nearby spindle, wherein the “spindle tendon” passes alongside the TO to attach to the aponeurosis, was found for 50% of cat EDB TO's, and 20 to 25% of the TO's in the other muscles. In cat EDB samples both TO's and spindles found in “tendon organ-spindle dyads” had larger cross-sectional areas at the equator than “solitary” units, and dyad TO's received the attachments of more extrafusal fibers than did solitary TO's. A number of the “solitary” TO's were found to be in line at a greater distance with spindles that lay along the extrafusal fibers inserting onto the TO. The possible developmental and functional significance of these findings is discussed.

(1964). The Amazing Patent on the Radiography of Paintings. Studies in Conservation: Vol. 9, No. 4, pp. 135-139.

Pressure changes induced by stretch or contraction of the tennuissimus and calf muscles of the cat were studied in relation to postulated mechanism for pressure activation of muscle spindles. Pressure was monitored through tubing filled with low-viscosity silicone oil connecting a hypodermic needle tip to a low-volume displacement transducer. Distribution of changes was detected by moving the needle to different sites in the muscle. Both stretch and total contraction produced essentially uniform pressure increases throughout the muscle. In fractional contractions, including those of single motor units, the center of contraction was marked by strong increases in pressure and the peripheral zones by weaker biphasic and negative changes. Over much of the muscle no change was detectable during contraction of a motor unit. In general the strongest gradient of pressure change seemed directed perpendicular to the axis of the contracting unit. It was concluded that conditions favoring the operation of a pressure mechanism in the spindle might exist in subtotal, but not in total contraction of the muscle.

(1958). The Radiography of Panel Paintings by Electron Emission. Studies in Conservation: Vol. 3, No. 4, pp. 175-182.

(1974). The Future of Radiography. Bulletin of the American Institute for Conservation: Vol. 14, No. 2, pp. 78-80.

As is well known, radiography provides a means for non-destructive analysis in many fields outside of medicine and medical research. Perhaps the industrial applications have received the most publicity, but x-rays have been similarly employed in such fields as archaeology, paleontology, geology, biology, conchology, zoology, and entomology. One of the best known non-medical and non-industrial uses of radiography is in art museums, where paintings are examined for analysis of the paint, canvas, paper, or wood base. Quite recently similar investigations have been made in the field of philately, or stamp collecting. A postage stamp consists basically of a design printed on a small piece of thin paper. It is important to the collector to be able to differentiate various characteristics of stamps. These include: (1) the method of printing, such as intaglio, letterpress, offset, photogravure, or other process; (2) the type of paper—woven, laid, ribbed, pelure, etc.; (3) watermark, if any, in the paper. Such inf...

By reconstructing tendon organs in detail from serial cross sections, a prediction is made on how these sensors might affect their nerve endings during changes in tension at musculotendinous junctions. Tendon organs are composed of specialized encapsulated fascicles of dense collagen which are offshoots from the primary tendon of origin or insertion of a muscle. Fascicles project into the muscle mass on their way to becoming attached to a bundle of extrafusal muscle fibers. The main spur of dense collagen rapidly divides into fine bundles with septa between. Within this encapsulated region, branches of the entering sensory nerve intertwine among the fine bundles of collagen fibers via the septa. Towards the muscle end of the tendon organ, these fine bundles reorganize again into heavy, dense bundles before insertion of extrafusal muscle fibers. The hypothesis is presented that the spaces between collagen bundles in a relaxed tendon organ might spread open reducing pressure upon nerve endings lying between; during tension, these bundles would straighten and crowd together, leading to compression of nerve endings. Variable compression of nerve endings would excite electrochemical events in sensory axons; thus, tension information would be coded and transmitted to the central nervous system. The arrangement of a tendon organ in series with muscle fibers would imply that the organ sampled tension primarily of that group of extrafusal muscle fibers attaching to the organ.

Golgi tendon organs from human, cat and rat extensor digitorum brevis muscles are compared in structural design. Microscopic studies reveal that these receptors appear to be very similar in structure, suggesting close functional similarities even though they are largest in man, intermediate size in cats and smallest in rats. This contrasts with similar observations on the structure of muscle spindles which show strong differences in respect to the insertion of intrafusal muscle fibers thereby implying species specialization of response characteristics to intramuscular tensions and pressures. Reconstructive drawings of human tendon organs from serial sections suggest how sensory endings may be affected by tensions at the musculotendinous junctions due to stretch or contraction of motor units. Finely divided collagen bundles appear to compress and distort nerve endings lying between them, thus inducing the generation of spike discharges.

The effects of acute stretch, laterally applied pressure, and exterfusal contraction upon the morphology of spindles in cat muscles have been studied by making measurements from serial histological sections. Cross-sectional areas of bag and chain intrafusal fibers were taken and the circumferences of spindle capsules measured at the equatoriallevel. From these area values the relative effects on length of the measured structures were inferred. 1. Stretch was found to lengthen the capsules and both bag and chain fibers. 2. Contracture induced by use of the drug ryanodine was accompanied by shortening of both bag and chain fibers. 3. Stretch was still effective in the presence of full contracture. 4. Pressure applied to the lateral surface of the muscle affectedboth bag and chain fibers. These findings taken with other considerations demonstrate the anatomical basis for the mechanism that is commonly assumed to cause the acceleration in discharge from primary and secondary endings with stretch and the “pause” with contraction of the gross muscle. The relation to a possible pressure sensing mechanism for secondary endings is discussed.

The manner of insertion of intrafusal (IF) fibers of muscle spindles has been studied in serial histological sections of spindles from hindlimb muscle of the cat, opossum, mouse, rat, bat and gibbon. Four basic types of IF terminations in relation to the capsule were recognized: (A) direct insertion into the capsule; (B) strong lateral attachments to the capsule, though the fiber may continue beyond the capsule; (C) termination in the connective tissue beyond the limits of the capsule; (D) free extension of the fiber beyond the capsule. Bag fibers in all species generally extended beyond the capsule. The pattern of chain fiber insertion, however, varied with the species. Most rat spindles, for example, followed the D pattern, those in the cat pattern A, and the gibbon chiefly A and B. The bearing of these findings upon a postulated mechanism by which spindles may detect intramuscular pressures, as changes in length, is discussed.

The suggestion is made that the mammalian muscle spindle may serve in part as a pressure sensor. Pressure acting nonuniformly on the spindle would express the intracapsular fluid distad, thus elongating the capsule. "Intracapsular fibers," those intrafusal muscle fibers inserting into the capsule, would be lengthened, whereas "percapsular fibers" passing beyond the capsule would be relatively unaffected. Since "flower-spray" terminals are preferentially associated with the smaller intrafusal fibers, they would chiefly be concerned with the pressure sensing mechanism. Observations in support of this hypothesis are given.

Two methods are described. (1) Low-voltage radiography. (2) Electron emission radiography. For lowvoltage radiography an X-ray tube with a beryllium window must be used, and 4 to 7 kilovolts is recommended. The film cannot be used in its paper envelope because this would register its own image. The bare film is placed, emulsion side up, in a vacuum register board with the paper to be examined on top of it. Over these is laid a thin sheet of cellulose acetate. Exposure is made through this thin sheet. Loading and exposure must be carried out in complete darkness. The successful radiograph should show the structure of the paper in good contrast. The film used is either Kodak Industrial X-ray film or Kodak Contrast Process Ortho film. For electron emission radiography high-voltage X-rays (200-250 kilovolts) are used. These do not themselves register the image on the film, but cause electrons to be given off from metals in contact with the film. The image is made by the electrons thus emitted. For the radiography of paper the high-energy X-rays strike a sheet of lead. The lead emits electrons uniformly, which are partly absorbed by the paper. Those that pass through the paper register on the film. All three layers, lead, paper, and film must be in very close contact and therefore a vacuum cassette is used. The film is the same as for low-voltage radiography. If metallic pigments are present as a design on the paper, these will give an image in low-voltage radio graphy, but not in electron emission radiography.

(1963). Infrared Luminescence in the Photographic Examination of Paintings and other Art Objects. Studies in Conservation: Vol. 8, No. 3, pp. 77-83.

Ordinary X-radiography of a painting on metal is unsatisfactory because the X-ray absorption of the thin film of paint is negligible compared to the absorption of the metal plate. Electron radiography, however, used on such a painting, gave a good image, revealing a ruff collar and lace head-dress which had been painted over. The technique is to place the film, emulsion side down) in very close contact with the paint surface, and to irradiate with high-energy X-rays through the film. These X-rays have only a small fogging effect on the film, but when they strike metallic pigments in the paint they cause electrons to be emitted which can travel the short distance to the film, and there register an image. An infra-red exposure is shown for comparison. Details of a sample electron radiograph: 200 kilovolts at 10 millamps for 3 minutes. X-ray tube distance 1 metre. Film: Kodak Industrial X-ray film, Type M (Single-coated). Filter 8 mm. Copper.

Just ~hout every conservat9r has had dental radiographs made at his dentist's office, but how many have considered the possibilities of using this same equipment for the radiography of museum objects? The tube head can be positioned for just about any direction of the central ray--an advantage one does not have with the fixed position of the typical museum x-ray installation or even with the medical x-ray unit. This versatility is most helpful when examining fragile ceramics that might be damaged by positioning them in unnatural positions.