Very small quantities of foot-and-mouth disease virus can only be detected by inoculation of a susceptible host. In general, the most sensitive host is one to which the particular virus strain under investigation has been adapted either by passage under natural or field conditions or by serial passage under experimental or laboratory conditions. For example, the maximum infective dilution of a bovine strain of virus may be from ten to one hundred times greater for cattle than for guinea-pigs, and, conversely, a guinea-pig-adapted strain may be more infective for guinea-pigs than for cattle (Henderson, 1949). Brooksby (1950) has recorded observations, based on experiments carried out under controlled laboratory conditions, on two strains of virus recovered from field outbreaks in swine which showed a marked degree of species adaptation to swine. An exception would appear to be the use of 1-week-old unweaned mice, for Skinner (1951) has shown by titration experiments that intraperitoneal inoculation of such mice with certain virus strains of cattle or guinea-pig adaptation gives as high an end-point as inoculation of the tongues of cattle or of the plantar pads of guinea-pigs respectively. This does not happen if older mice are used. Conversely, strains of virus passaged serially in unweaned mice show higher titres when titrated in such mice than when titrated in cattle or guinea-pigs.Most workers would agree that when cattle are employed intradermal inoculation of the tongue is the most certain method of producing infection, but there is little information available on how much more virus is required to produce an infection if given by another route. Bedson, Burbury & Maitland (1925) inoculated guineapigs subcutaneously, intramuscularly, intraperitoneally and by scarification and intradermal inoculation of the plantar pads. They found the subcutaneous route very uncertain and, of the others, preferred intradermal injection of the pads but noted that scarification of the pads was almost as satisfactory. Working in this laboratory, Aramburu (1949) has shown by quantitative studies that multiple intradermal tracking is the most sensitive method of plantar-pad inoculation in the guinea-pig. Brachmann (1925) compared intradermal inoculation of the plantar pads with intraperitoneal and subcutaneous inoculation. He found that less virus was required to infect by the intradermal route.In seven experiments with cattle, six strains of virus have been used for the quantitative comparison of intradermal inoculation of the tongue with subcutaneous inoculation; in one experiment intracutaneous inoculation was also

Quantitative studies have been made of the survival of foot-and-mouth disease virus in beef and beef offals after storage at temperatures employed in the imported-meat trade.The survival of virus is closely associated with the hydrogen-ion concentration of the tissue; thus the acidity of rigor mortis of muscular tissue rapidly causes inactivation. Quick-freezing of beef suspends acid formation and active virus was demonstrated for so long as the meat was kept frozen.Thawing of quick-frozen meat initiates the suspended acid formation at an accelerated rate and rapidly produces a medium unsuitable for virus survival.Liver, kidney, rumen, lymph node and blood from diseased cattle have all been shown to be highly infective and to remain so if stored frozen. Acid formation in these tissues and in blood is not on the same scale as in muscle, and prolonged survival of virus is more likely even with delay in freezing and after thawing. This remains true of lymph node and of residual blood in vessels of a carcass in which the development of rigor mortis is complete.Feeding of infective offal to swine under experimental conditions resulted in the appearance of the disease.The significance of these observations is discussed in relation to the distribution of these products constituting a risk of spreading foot-and-mouth disease.We are indebted to Dr Ian A. Galloway, Director of this Institute, Mr L. B. A. Grace, Chief Technical Adviser on Meat Inspection of the Ministry of Food and Mr R. Bremner, Chief Executive Officer of the Meat Importers' National (Defence) Association, Ltd., for their help and advice while this work was in progress.It is a pleasure to acknowledge the technical assistance of Mr W. J. Brownsea.

Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and thermal desorption Gas Chromatography-Mass Spectrometry (GC-MS) allow for absolute quantification of a wide range of atmospheric volatile organic compounds (VOCs) with concentrations in the ppbv to pptv range. Although often neglected, routine calibration is necessary for accurate quantification of VOCs by PTR-MS and GC-MS. Several gas calibration methods currently exist, including compressed gas cylinders, permeation tubes, diffusion tubes, and liquid injection. While each method has its advantages and limitations, no single technique has emerged that is capable of dynamically generating accurate concentrations of complex mixtures of VOCs over a large concentration range (ppbv to pptv), is technically simple and field portable, and affordable. We present the development of a new VOC calibration technique based on liquid injection with these features termed Dynamic Solution Injection (DSI). This method consists of injecting VOCs (0.1–0.5 mM) dissolved in cyclohexane (PTR-MS) or methanol (GC-MS) into a 1.0 slpm flow of purified dilution gas in an unheated 25 mL glass vial. Upon changes in the injection flow rate (0.5–4.0 μL min^&minus;1), new VOC concentrations are reached within seconds to minutes, depending on the compound, with a liquid injection flow rate accuracy and precision of better than 7% and 4%, respectively. We demonstrate the utility of the DSI technique by calibrating a PTR-MS to seven different cyclohexane solutions containing a total of 34 different biogenic compounds including volatile isoprenoids, oxygenated VOCs, fatty acid oxidation products, aromatics, and dimethyl sulfide. In order to validate the new DSI method, a GC-MS and PTR-MS calibration intercomparison with VOC standards generated by dynamic dilution of NIST traceable permeation tubes (<i>&alpha;</i>-pinene, acetone, and ethanol) and a compressed gas cylinder (acetaldehyde) was made. The results revealed that while calibration of acetone is comparable between the methods, calibration curve slopes for other VOCs obtained by using permeation tubes and the compressed gas cylinder are lower than those obtained by the DSI technique by up to a factor of 2. This implies that concentration measurements of some VOCs may be overestimated using permeation tubes and/or compressed gas cylinders for calibration. Because of its high accuracy and precision, small size, low cost, and simplicity, we conclude that the Dynamic Solution Injection method will be of great use to both laboratory and field VOC studies

No abstract

Abstract. Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and thermal desorption Gas ChromatographyMass Spectrometry (GC-MS) allow for absolute quantification of a wide range of atmospheric volatile organic compounds (VOCs) with concentrations in the ppbv to pptv range. Although often neglected, routine calibration is necessary for accurate quantification of VOCs by PTR-MS and GC-MS. Several gas calibration methods currently exist, including compressed gas cylinders, permeation tubes, diffusion tubes, and liquid injection. While each method has its advantages and limitations, no single technique has emerged that is capable of dynamically generating known concentrations of complex mixtures of VOCs over a large concentration range (ppbv to pptv) and is technically simple, field portable, and affordable. We present the development of a new VOC calibration technique based on liquid injection with these features termed Dynamic Solution Injection (DSI). This method consists of injecting VOCs (0.1-0.5 mM) dissolved in cyclohexane (PTR-MS) or methanol (GC-MS) into a 1.0 slpm flow of purified dilution gas in an unheated 25 ml glass vial. Upon changes in the injection flow rate (0.5-4.0 µl min −1 ), new VOC concentrations are reached within seconds to minutes, depending on the compound, with a liquid injection flow rate accuracy and precision of better than 7% and 4% respectively. We demonstrate the utility of the DSI technique by calibrating a PTR-MS to seven different cyclohexane solutions containing a total of 34 different biogenic compounds including volatile isoprenoids, oxygenated VOCs, fatty acid oxidation products, aromatics, and dimethyl sulfide. We conclude that because of its small size, low cost, Correspondence to: K. J. Jardine (jardine@email.arizona.edu) and simplicity, the Dynamic Solution Injection method will be of great use to both laboratory and field VOC studies.