Abstract
1. Serum of various animals preserves the motility of nagana trypanosomes better and longer than salt solution. 2. To act best in this way the serum should not be diluted more than 2 to 4 times. Undiluted serum is perhaps best. 3. Serum filtered through a Berkefeld filter, bottled aseptically, and kept in the ice box preserves this activating property apparently undiminished for many months. 4. Serum preserves the motility of trypanosomes better than "Sals physiologicum" of Merck, and better than the Ringer solutions of Meltzer and Carrel. 5. Serum preserves the normal morphology of trypanosomes better than the Ringer solutions tested. 6. The infectiousness of trypanosomes suspended in cattle serum was preserved at room temperature for at least 8 days. 7. The vitality of the trypanosomes in serum was seemingly better preserved at room temperature than at ice box temperature. 8. Serum incubated with atoxyl does not transform it into a toxic substance. 9. Serum does not bind paraminophenylarsenoxyd, for trypanosomes suspended in serum are often immobilized more quickly by paraminophenylarsenoxyd than trypanosomes suspended in salt solution. 10. Serum is suitable for suspending trypanosomes for certain experiments in vitro, and with proper precautions may be employed for transporting virus from laboratory to laboratory.