Trypanosoma equiperdum used in this investigation was obtained from rats serially inoculated with the blood of an infected guinea pig made available through

the kindness of Dr. D. B. McMullen of the Army Medical Service Graduate School. Blood was drawn from the heart into a 10 ml. syringe containing about 1 cc. of 6% solution of sodium citrate and subsequently delivered into a centrifuge tube and centrifuged three times. The first centrifugation was carried out for approximately 8 minutes, after which the plasma containing white cells and trypanosomes was decanted into a second tube and centrifuged for about 10 minutes, thereby throwing down the white cells and platelets. The serum after the second centrifugation was decanted into a new tube and centrifuged for the third time for approximately 20 minutes. After the third centrifugation, the supernatant containing the trypanosomes was delivered into another tube containing about 1 cc. of 1% osmium tetroxide solution (fixative) buffered at pH 7.25 according to the method of Palade (1952). The organisms were fixed for 20-30 minutes, washed, dehydrated, infiltrated and embedded. Infiltration was carried out using a methacrylate monomer mixture consisting of 72% N-butyl methacrylate and 28% methyl methacrylate with a catalyst added (Luperco, 0.2 gm./10 cc.). The infiltrated organisms to be embedded were put into number 4 gelatin capsules and placed in an oven and allowed to polymerize for 8 hours at 48? C. The embedded specimens were sectioned with an International Minot rotary microtome, approximately 0.025 micron thick, and ribbons so obtained were mounted on copper-mesh grids previously covered with a supporting film prepared from a 2% solution of celloidin in amyl acetate. Observations were made, without removing the embedding mixture, with an RCA model EMU-2B electron microscope. The electron micrographs were taken at an original magnification of 3700 or 5700 and thereafter enlarged photographically