This study is an investigation of the heat resistance of the spores of B. botulinus and the effects of several variable conditions which are ultimately responsible for their death. The conditions reported are: the effect of hydrogen and hydroxyl ion concentrations on thermal resistance and the effects of numbers of spores, desiccation, spore age and the presence of sodium chloride. A number of other factors and the intimate nature of the process of killing by heat under different conditions, and the laws governing it, are being studied. In addition to the purely academic aspects of the problem which this work covers, it is designed to furnish adequate criteria for the practical problems of sterilization and to insure the safety of processed foods with respect to botulism. THERMAL DEATH RATE OF DIFFERENT STRAINS For the purpose of our subsequent work and in order that the results obtained might have a practical application, it was necessary to determine the thermal resistance of the spores of all the available strains and to devote our attention to the most resistant one. There were sixteen strains in our laboratory at the time this work was begun, all of which were studied. Strain 1. From the Museum of Natural History, New York; original source unknown; old laboratory strain of low virulence. Strain 2. From the College of Physicians and Surgeons, New York; original source unknown; low virulence. Strain 3. From San Jose, Calif. Isolated by Dickson from the crop of a chicken that died after eating home-canned string beans. The same beans had caused the death of one person. The strain was virulent. Strain 4. From Hillsboro, Ore. Isolated by Dickson from the gizzard of a chicken that died after eating home-canned corn. The same corn had poisoned one person and about 50 chickens. The strain was virulent.

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Martin sent me several species of beetles which he had collected on fungi in the neighborhood of Iowa City, Iowa, and they proved to be Hister lecontei Mars., on Mutinus elegans, August 11 (probably not feeding on the fungus); Mycetophagus punctatus Say feeding on Polyporus radicatus, August 11; Mycotretus pulchra Say on Russula irrescens, July 4;

Packard in his "Forest Insects" records B. aerosus as occurring on oak early in summer in Maine and late in May near Providence, R.I., and states t h a t Gillette (Canad. Ent. July, 1887) reared i t from larvx in poplar leaves, the mines being finished in October and the beetles appearing early the following May. Concerning B. ovatus, this species is recorded by Packard as follows "on laurel oak; imago issues latter part of April and early May (Riley's unpublished notes) ." Gillette also reports rearing the beetle from a larva mining a leaf of either red or black oak. Felt (N. Y. State Mus. hZem. 8; 2, p. 512-3) states t h a t B. aerosus was taken while feeding on elm during the latter half of May, and that B. ovatys was common on scrub oak the latter part of May and June. Blatchley in his ' b~o~e o~t e r a of Indiana" records aerosus as throughout the state, frequent, May 16-June 18, occurring on oak, hickory, elm and ovatus also as throughout the state and frequent, May 16-July 13, on oak in the leaves of which the larvz dwell. According t o Smith (Rept. N. J. State Mus. 1909) aerosus is found throughout New Jersey, not rare, on oak, May, June and ovatus is common throughout the state, June t o August on oak. Burke (U. S. Dept. Agric. Bull. NO. 437, 1917) summarizes the distribution, common habits and host trees of the genus Brachys as follows:-"Eastern and Central States, leaf miner in leaves : Populus ?, alder (Alnus), Fagus ?, chestnut (Castanea), oak (Quercus) ,