The acoustical properties insertion loss, reflection loss, and sound speed were measured on a series of fresh and subsequently formalin immersed human skulls. Measurements were made in the frequency range from 0.25 to 6 MHz. Most studies were restricted to an upper frequency limit of 2.2 MHz. An axisymmetric focused beam configuration was used as the sound source for the measurements and the receivers were small disk-type (3-mm-diam) piezoelectric ceramics. The geometric and temporal character of the focused beam was studied as a consequence of passage through the skull sections. Some skulls were sectioned so that their individual layer components could be studied. A simple three-layer analytical model seems to explain the major aspects of insertion and reflection loss. The dominant feature in determining human adult skull losses is the middle layer (diploe) of cancellous bone. This study corroborates previous work on insertion loss as a function of frequency for composite skull. The study provides new quantitative information on the acoustic scattering properties of diploe, sound velocity, and dispersion in composite skull and its components, attenuation coefficients in skull components and sound-beam distortion and shifts after transmission through composite skull. We conclude that with selection of appropriate frequencies (0.5-1.0 MHz) and beam configuration it will be possible to perform clinically significant transkull diagnostic imaging and interrogation in the adult human brain.

The effect of temperature and thermal dose (equivalent minutes at 43 degrees C) on ultrasonic attenuation in fresh dog muscle, liver, and kidney in vitro, was studied over a temperature range from room temperature to 70 degrees C. The effect of temperature on ultrasonic absorption in muscle was also studied. The attenuation experiments were performed at 4.32 MHz, and the absorption experiments at 4 MHz. Attenuation and absorption increased at temperatures higher than 50 degrees C, and eventually reached a maximum at 65 degrees C. The rate of change of tissue attenuation as a function of temperature was between 0.239 and 0.291 Np m-1 MHz-1 degree C-1 over the temperature range 50-65 degrees C. A change in attenuation and absorption was observed at thermal doses of 100-1000 min, where a doubling of these loss coefficients was observed over that measured at 37 degrees C, presumably the result of changes in tissue composition. The maximum attenuation or absorption was reached at thermal dosages on the order of 10(7) min. It was found that the rate at which the thermal dose was applied (i.e., thermal dose per min) plays a very important role in the total attenuation absorption. Lower thermal dose rates resulted in larger attenuation coefficients. Estimation of temperature-dependent absorption using a bioheat equation based thermal model predicted the experimental temperature within 2 degrees C.

Table 1. Effects of amino acids upon the time required for abscission of unfertilized ovaries of two varieties of tobacco. The figures show average time in hours from anthesis to completion of abscission. Lizard's Tail Little Turkish 0.01M 0.1M 0.01M 0.1M Methionine Control (water) 99 93 176 165 Table 1. Effects of amino acids upon the time required for abscission of unfertilized ovaries of two varieties of tobacco. The figures show average time in hours from anthesis to completion of abscission. Lizard's Tail Little Turkish 0.01M 0.1M 0.01M 0.1M Methionine Control (water) 99 93 176 165others is uncertain at present, but it is generally agreed that indoleacetic acid plays a major role in the control. The dissolution of the middle lamella of the cell wall during abscission was described first by Lee (3). Facey (4), through microchemical tests, characterized the dissolution as a change of calcium pectate into pectic acid which, in turn, is changed to water-soluble pectin. Recently Cormack (5) has emphasized the calcium pectate character of the cementing layer between cells. Ordin, Cleland, and Bonner (6) have reported that the methyl carbon atom of labeled methionine is rapidly incorporated into the pectic materials of cell walls of Avena coleoptile sections, and Byerrum and Sato (7) have also reported the incorporation of the methyl group of methionine in pectin isolated from radish plants. These observations suggest that methylation of the carboxyl groups of adjacent pectin molecules may be involved in the splitting of calcium bridges leading to abscission and that the amino acid methionine may serve as a methyl group donor. Experimental evidence indicates that an amino acid factor does, in part, control abscission.Two varieties of Nicotiana tabacum, namely Lizard's Tail and Little Turkish, were grown under uniform greenhouse conditions and used as experimental plants. Various aqueous solutions of L-amino acids (DL-methionine, DL-leucine, DL-valine), after being adjusted to pH 6.0, were injected directly into the unfertilized ovaries of flowers at the time of anthesis by means of glass tubing drawn to a fine point. In 24 hours, 0.15 to 0.2 ml of the solution were 10 JANUARY 1958

W rITH the contemporary development of surgical methods of treating the symptoms of painful, psychiatric, and basal ganglion disorders, the neurosurgcon is frequently called upon to produce a focal destructive lesion in the nervous system. The universal and obvious objective is to create a localized lesion in the desired area with no damage to adjacent or intervening tissues. Recorded experiences of neurosurgeons attest to the fact that this ideal has not yet been attained. Paraparesis and bladder dysfunction following anterolateral chordotomy, vegetation following prefrontal lobotomy, and hemiplegia following surgical treatment of basal ganglion disorders are examples of damage to adjacent tissues known to all neurosurgeons. Damage to blood vessels (including those within the site of the lesion) at time of operation may increase the operative morbidity and render it impossible to evaluate the effect of a focal ablation. Stereotaxically placed electrocoagulative lesions have frequently resulted in death from hemorrhage.As the result of animal experimentation 1-4,6 we believe that the use of ultrasound in making human focal destructive lesions will overcome some of these objections. A focussed beam of ultrasound can be used to produce selective, accurately localized lesions in the central nervous system which are quantitatively reproducible from one animal to another. Discrete lesions can be produced without destruction of blood vessels. A lesion in the depths of the brain can be effected without disturbance of intervening tissue. Accurate localization is accomplished by focussing a fine beam of ultrasound in the region to be treated. The nature of the destruction depends upon the intensity and duration of the exposure.The term "ultrasound" refers to sounds whose frequency (pitch) is above the range of human audibility (15,000 to ~0,000 cycles per second). M:ost of the work up to the present time has been accomplished at a frequency of one * Partially supported by Contract Nonr 336(00), NR 119-075 with the Physiology Branch of the Office

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