A F2 population derived from a cross between European Large White and Chinese Meishan pigs was established in order to study the genetic basis of breed differences for growth and fat traits. Chromosome 4 was chosen for initial study as previous work had revealed quantitative trait loci (QTLs) on this chromosome affected growth and fat traits in a Wild Boar x Large White cross. Individuals in the F2 population were typed for nine markers spanning a region of approximately 124 CM. We found evidence for QTLs affecting growth between weaning and the end of test (additive effect: 43.4 g/day) and fat depth measured in the mid-back position (additive effect: 1.82 mm). There was no evidence of interactions between the QTLs and sex, grandparents or F1 sires, suggesting that the detected QTLs were fixed for alternative alleles in the Meishan and Large White breeds. Comparison of locations suggests that these QTLs could be the same as those found in the Wild Boar x Large White cross.

A very simple and cheap design is described that can be used up to 1 000 atm. The stainless steel pressure chamber is provided with six insulated Pyrotenax leads and a permeability bridge for measuring mechanical changes. It has been used for recording the tension developed by a stimulated muscle but could be readily adapted to suit other experimental requirements.

A sensitive moving coil galvanometer is described which is stable enough, under ordinary laboratory conditions, to allow a 20- to 50-fold magnification of its movements. The magnified deflexion is read on a standard microammeter. Negative feedback from the output of a photoelectric amplifier to the galvanometer circuit allows the sensitivity to be diminished as required, with corresponding gain in stability. The galvanometer is strongly overdamped, but its short natural period gives it a reasonably short deflexion time (a few seconds). Tests of performance show that the average error of a single deflexion, in spite of the manifold disturbances of a busy laboratory, corresponds to about 0.002-0.004 μV. In a quiet place it would be considerably less.

The thermopile previously described by Downing, Gerard and Hill (1) for the measurement of the heat-production of nerve had four chief disadvantages : ( a ) it gave a relatively small E. M. F. per 1° C., only about 1800 microvolts altogether, about 4½ per couple; in another of these thermopiles, with a smaller number of couples, 1° C. evoked about 9 microvolts per couple. ( b ) This E. M. F. fell off rather quickly, reaching zero within 45 seconds, owing to rapid heat-conduction, ( c ) The temperature of the thermopile took a very long time to settle down, after placing the nerves upon it, viz., about 4 or 5 hours, ( d ) It was very difficult to construct. Of these, ( a ) was due partly to the small length of each couple exposed to the nerves, and partly to the fact that the wire was in contact on its other side with a relatively large mass of insulating material in the wedge on which it was wound; ( b ) was due partly to the neigh-bourhood of this mass of insulating material, which rapidly cooled the wires and nerve, and partly to the conduction of heat away along the wires to the cold junctions which rather soon warmed up; ( c ) was due to the use of a large mass of insulator, which—being a poor heat conductor—allowed only a very slow equalisation of the temperature differences inevitably set up in the initial handling required in placing the nerve in position; ( d ) was chiefly due to the difficulty of fitting the 3 (or 4) wedges exactly together, without gaps, and of joining their very line wires in series. A first attempt to improve the thermopile in these respects was made as follows. To avoid contact of the wires, in the neighbourhood of the junctions, with a mass of insulating material, the wedges on which the wire was wound were milled out along their narrow ends, as shown at ( a ) in the accompanying figure. The wires passed across the gap, the junctions between silver and constantan being in the middle. In this way about 1½ mm. of wire, i. e., ¾ mm. on either side of the junction, was exposed to nerve on one side without being in contact with anything but air on the other. The wedges were of amber, which will stand baking, and the wires were painted with an alcoholic solution of an artificial resin (“ Elo ”) and baked, the process being repeated several times, until a sufficient layer of insulating varnish had been deposited. The use of this varnish has been described already (2, p. 127). It forms a thin, delicate and almost glass-hard sheet of wires and insulator. After mounting the wedges and finishing the carrier a very thin layer of shellac was painted over the (“Elo”) and any small gaps at the edges were filled up with shellac/working under a Zeiss stereoscopic microscope. Then a mixture of paraffin wax and beeswax was spread very gently and thinly over the surface, and melted on with a minute gas flame. This as described in (2), p. 129, renders the surface waterproof. The ends of the grooves in the wedges were then blocked by the paraffin wax, so that water should not get in, the space between the solid wedge and the wire sheet being thereby rendered air-tight. The mass of insulator employed on the carriage of the thermopile was cut down as much as possible, so as to ensure a more rapid equalisation of temperature.

The Journal of PhysiologyVolume 68, Issue 1 p. 1-18 ArticleFree Access The electric response of nerve to two stimuli William R. Amberson, William R. AmbersonSearch for more papers by this authorA. C. Downing, A. C. DowningSearch for more papers by this author William R. Amberson, William R. AmbersonSearch for more papers by this authorA. C. Downing, A. C. DowningSearch for more papers by this author First published: 28 August 1929 https://doi.org/10.1113/jphysiol.1929.sp002591Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume68, Issue1August 28, 1929Pages 1-18 RelatedInformation

By means of a method involving the use of a fine hot wire, it is possible to determine very small and varying rates of flow of a fluid with great accuracy. The lag due to inertia of recording instruments is almost entirely eliminated.

A new moving magnet galvanometer of the Thomson type, having a figure of merit up to 35,000 and considerable stability of zero, is described. Its simple design and its small size have not only greatly increased the utility of the instrument, but considerably lowered the cost of its manufacture.

The figure of merit of a sensitive galvanometer depends to a preponderant degree upon the construction of its moving system. By providing the Broca galvanometer with a light magnet system of astatic type, containing four or eight magnets of cobalt steel, it is possible to increase the figure of merit about sixteen times. A suitable mirror enables the spot of light to be read accurately at a distance of several metres and the good astatic qualities of the moving system ensure considerable stability of zero even without magnetic shielding. The construction of the instrument has been slightly modified to allow the insertion of this system.