The strain of L. icterohemorrhagiae on which the following observations were made was received in 1925 from Dr. Hideyo Noguchi, who isolated it in New York from a wild rat (1). It is know in the medical literature as “American No. 2.” While in our possession, it has been maintained in cultures in Noguchi's semisolid medium, consisting of one part of rabbit's serum, one part of 2 per cent nutrient agar, and eight parts of salt solution. It has only occasionally been passed through guinea pigs, and has shown a moderate degree of virulence for these animals.
On February 19, 1929, twelve tubes of fresh medium were inoculated from a stock culture. The plugs were dipped into boiling paraffine to prevent evaporation and contamination with molds, and the cultures were left standing at room temperature (average 80°F.) in the dark, for over nineteen months.