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It has been definitely established (Waksman, 1941; Waksman and Horning, 1942) that fungi capable of producing anti-bacterial substances are widely distributed in nature and are not limited to any one or more taxonomic groups. Such fungi can be readily isolated from soils, manures, composts, and dust by the use of appropriate bacteria-enriched agar media. Out of some 160 antagonistic fungi thus isolated, two organisms were selected for further study, because of their outstanding capacity to produce in culture media substances which inhibit in rather high dilutions the growth of various bacteria. These two organisms were Aspergillus fumigatus Fresenius, of which 16 strains were isolated from different soils and composts, and Aspergillus clavatus Desmazieres, represented by 3 isolations. The methods of testing the antibiotic action of the culture filtrates of these organisms have been described in detail elsewhere (Waksman and Homing, 1942). This paper deals specifically with the formation, concentration, and isolation of the antibiotic substances produced by these two fungi under different conditions of culture and nutrition. ASPERGILLUS FUMIGATUS When grown in simple synthetic media A. fumigatus produces an antibiotic substance, which has been designated as "fumigacin" (Waksman, Horning and Spencer, 1942). The medium used most extensively for this purpose was that of Czapek-Dox or a glucose-nitrate solution, which consists of 40 g. glucose, 3 g. NaNO3, 1 g. KH2PO4, 0.5 g. KCl, 0.5 g. MgSO4 7H20, 0.01 g. FeSO4.7H20, and 1000 ml. tap water.-The antibiotic substance was found to be produced in this medium during the early stage of growth of the organism: its presence could be demonstrated even within 3 days incubation at 28°C; it reached a maximum in 7-8 days, and then gradually disappeared on further incubation. The reduction in activity is due either to the destruction of the active substance or to its transformation into an inactive or at least a less active type of compound. In view of the recent announcement made by Oxford and Raistrick (1942) that fumigatin, a maroon-colored pigment produced by A. fumigatus, also has antibacterial properties, it was desirable to establish first the possible relation between the nature and formation of fumigatin and fumigacin, as well as their chemical and biological differences. This can be done by comparing the results on fumigacin obtained in this laboratory, with those on fumigatin reported from

IntroductionAlthough viruses eause many plant diseases, little is known regarding their metabolism since they apparently multiply only in living tissue. Here it is difficult to differentiate between the metabolism of a host and that of a pathogen. Multiplication of viruses in vito is a well recognized fact and thermal inactivation in vivo of a few viruses has been definitely established. No other method for the inactivation of virus in vivo has been demonstrated experimentally.In this study on virus metabolism, a knowledge of the nitrogen metabolism of normal tobacco plants and the discovery that nitrogen supplied to a virus-infected plant had an effect on virus concentration (19) have made it possible to distinguish to some extent between the anabolic and katabolic processes involved. It is well known (14, 24) that in mature leaves of a nitrogen-deficient plant proteins are hydrolyzed and proteolytic decomposition products liberated. These are translocated to the growing point where they supply the meristem with materials necessary for protein svnthesis. A studv of the effect of withholding nitrogen from a tobacco plant diseased with tobacco mosaic on the total quantity and specific biological activity of virtus within the plant has thrown light on the following questions: Is 24th day the nitrogen-fed plants were nearly 5 times the size of those deficient in nitrogen. During this 24-day period, the green weight of nitrogenfed plants increased about 18-fold, whereas that of nitrogen-deficient plants increased less than 4 times. A portion of this increase in nitrogen-deficient plants was probably due to the reserve of unassimilated nitrogen present in these plants at the time they were transferred to the minus-nitrogen treatment. SPENCER: TOBACCO-MOSAIC VIRUS AND NITROGEN DEFICIENCYData pertaining to the total-protein content andl the virus-protein content of aliquots of juice from the two sets of plants at each harvest are recorded in table III. In plants receiving nitrogen, the mg. of total protein per ml. of juice increased at first and then decreased slightly. The lowv protein contents recorded on the 16th and 24th day were probably due in part to the fact that each of these harvest days was preceded by one or more dark, cloudy days. The decrease in carbohydrate synthesis is accompanied by an accelerated hydrolysis of stored proteins. In

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