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In the preceding paper of this series we have described an efficient and versatile apparatus for freeze-drying by vacuum sublimation. This apparatus makes it possible to dehydrate biological materials at low temperatures and, by the use of ionization gauges, to determine the end-point of dehydration of material maintained at temperatures ranging down to --80°C. It is so designed that different samples of the same material can be subjected simultaneously to various experimental conditions. Time, rate, and degree of drying have been shown to have a marked influence on the physical properties of lyophilized biological materials other than viruses by Elser, Thomas, and Steffen (1); Greaves and Adair (2); Flosdorf, Hull, and Mudd (3); Greaves (4) and others. Proom and Hemmons (5) have published working details for the freeze-drying preservation of a collection of more than 1500 strains of bacteria. Various methods of freezing, the degree of drying, and the effect of storage were tested by viability counts. Recently, Hutton, Hilmoe, and Roberts (6) have reported on the effects of these factors on the quantitative survival of Brucella abortus. Similar studies dealing with the survival of viruses have not been reported.The present investigations deal with the quantitative survival of influenz a virus suspensions, after repeated freeze-thaw cycles, freezing at various speeds, storage in the frozen state at various temperatures, and vacuum sublimation at various temperatures following different types of preliminary treatment. Subsequent investigations are planned which will be concerned with the effects of these factors on the survival of complex cells.

The elevation of serum lactic dehydrogenase (LDH) activity has been observed in association with a variety of diseases. Such elevations have been reported in humans with certain neoplastic diseases ( 1 :2) and in mice with spontaneous, induced and transplanted tumors(3,4). High LDH activity has also been observed in patients with several nonneoplastic disease states, such as diabetic acidosis, myocardial infarction and hepatitis( 2 ) , although the number of cases is small and comparative levels of activity between various non-neoplastic and neoplastic diseases have not been specified. I t is evident from such preliminary observations that a broad survey of a large variety of disease states is required in order to evaluate properly the clinical significance of changes in serum LDH levels and the usefulness of such determinations as a diagnostic tool. Furthermore, such a survey might suggest possible mechanism for alterations in serum LDH levels. I n this report, then, we are presenting the results of such a survey, consisting of 130 individuals free of evidence of clinical disease, and 338 unselected hospital admissions.Material and nzethod. Clotted venous samples from human subjects were used for this investigation. The blood was allowed to stand at room temperature for no longer than 30 minutes and then centrifuged to separate serum from blood cells. For LDH determination serum samples thus collected were diluted prior to analysis. The micromethod of Strominger and Lowry(5) was used for the determinaltion of level of enzyme activity and the results were recorded as millimoles of substrate oxidized per liter of serum per hour. Storing of uncentrifuged blood samples a t 4°C not over one day gave the same result as that obtained with samples kept at room temperature for 30 minutes or less. However? clotted blood samples which remained at room * These investigations were supported by the David May-Florence G. May Memorial Research Fund. temperature for as long as 60 minutes showed an increase in 1,DH activity by approximately 25% over those stored at 4OC or a t room temperature for no more than 30 minutes. Heparinized and oxalated blood samples also gave LDH values about 40 and 60% higher, respectively, than refrigerated or 30 mjinute samples. The latter were therefore excluded from the data herein presented. The data have been grouped by organ systems, with subclassification into disease groups, and, except for a graphic presentation of findings in myocardial infarction, are all recorded in Table I. Multiple determinations were made in many cases, but except for those with myocardial infarction, an average was taken in each instance.

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