An extensive literature dealing with the metabolism of bacteria has accumulated, but so far, little work has been carried out on the metabolic activities of the protozoa. The protozoologist's inability to grow the latter for many generations, has been and still is one of the difficulties in the way. The pathogenic protozoa that have been cultivated in pure culture with the greatest success are the hemoflagellates, or blood parasites, but the growth is scanty even after a number of days of incubation. Cultivation of Trypanosoma lewisi was carried out by McNeal and Novy 1 on a nutrient blood agar medium, and the same investigators 2 have also described methods for the growth of T. brucei, T. avium, T. laverani, and T. mesnili. Others who have worked in this field are Rogers,3 Longo,4 Nicolle,5 Row," Laveran and Pettit,7 Mathis,s Thomson,9 Ponselle,10 Luna,11 Noguchi and Lindenberg,12 Kligler,33 Leiva,14 and Pedroso,15 In no case, does it appear that the growth was sufficiently heavy for studies of metabolism. It was therefore necessary in our work to develop mediums not only for the preservation of stock cultures of Leishmania, but also for carrying out studies of the metabolism of the organism.