1. The resistance of erythrocytes of dogs to the hemolytic activity of cobra venom is increased after splenectomy.
2. This increased resistance was observed as early as 4 days after splenectomy and usually persisted for a period of about 3 weeks, when the resistance gradually decreased to normal or slightly beyond.
3. The decrease of resistance to the hemolytic activity of venom for the erythrocytes of splenectomized dogs following the primary increase is apparently coincident with the anemia following splenectomy. An intercurrent infection, such as distemper, tends to reduce the resistance of erythrocytes to venom.
4. An increased resistance of the erythrocytes to hypotonic salt solutions was found with all the splenectomized dogs in which these tests were made. Increased resistance to hypotonic salt solutions apparently persists for a longer period than the increased resistance to cobra venom.
5. As the lysis of erythrocytes by venom is dependent upon the presence of certain lipoidal substances within the cells, and as the spleen may exercise an influence over the lipoidal contents of corpuscles and serum, it is suggested that the increased resistance of erythrocytes to the hemolytic activity of venom after splenectomy is due to alterations in the lipoid content of the erythrocytes.