1. It is stated that the erythrocytes show a different cataphoresis in the same solution according to the species of the animals and the erythrocytes of the same animal in two different solutions. 2. The erythrocytes of the rabbit possess in 0,9% NaCl solution a positive charge unlike those of the other animals, while they are charged in the isotonic sugar solution most negatively charged. 3. The cataphoresis of the erythrocytes was observed under the microscope not only in the NaCl solution but in many other salt solutions. 4. The statement follows how the cataphoretic phenomena which the erythrocytes show in the isotonic solution of NaCl or cane-sugar are modified by the addition of several reagents. 5. A test is made showing the change of pH of different solutions after the addition of the erythrocytes. 6. It is demonstrated that some Cl-ions in solutions of NaCl or KCl are taken by the erythrocytes which in turn give off some HCO3-ions. 7. Of all the animals the efficiency of the erythrocytes to raise pH of some salt solutions, especially of acid salt solutions is the greatest in the rabbit and the least in the dog as far as they were examined. 8. On the other hand the erythrocytes of the rabbit have a weaker efficacy to neutralize an alkaline solution than those of the dog, guinea-pig or goat. 9. While the erythrocytes absorb some Cl-ions in an acid salt solution, they release these in an alkaline salt solution. 10. The strong efficiency of the rabbit erythrocytes to raise pH of some solutions is an important factor, the explanation, perhaps, being that they possess a positive charge in the salt solution unlike those of almost all other animals. Likewise the fact that the erythrocytes of the dog have a strong negative charge in the salt solution seems to bear upon their weak efficacy to neutralize an acid solution. 11. In order to explain the cataphoresis of the erythrocytes in the sugarsolution a hypothesis is offered concerning the permeability of the membrane of the erythrocytes. If the erythrocytes of the rabbit are thrown into a sugar solution which contains no electrolytes, there would occur a condensation of the cell membrane, so that it would hinder the passage of some anions, while the diffusion of cations goes on unaffected. On the other hand the permeability of the erythrocytes of the dog and cat seems to remain almost unchanged in the sugar solution as well as in the salt solution. For this reason the erythrocytes of the rabbit become in the sugar-solution strongly negatively charged, while those of the dog and cat remain weakly negatively charged. 12. Such solutions as 3,0% glycerine, 5,0% d-glucose, 5,0% laevulose, 9,5 % lactose and 2,0% glycocoll have the same effect as that of 9,5% canesugar solution on the cataphoresis of the erythrocytes. 13. The erythrocytes of the rabbit which have a strong power to neutralize an acid solution and are slightly positively charged in 0,9% NaCl solution resist the haemolytic effect of the acid more obstinately than those of other animals. On the contrary the crythrocytes of the goat which show a strong negative potential in 0,9% NaCl solution are most liable to the haemolysis caused by the acid. Generally speaking it seems probable that erythrocytes which are strongly negatively charged in the NaCl solution dissolve in an acid solution more easily than those weakly charged. 14. But in a solution of reserve acidity in which some substance acts as "buffer" the erythrocytes of the rabbit are most liable to haemolysis, while those of the goat and dog show a great resistance at least during the first few hours. 15. The erythrocytes of the dog are most easily dissolved in the alkaline solution. With this special exception, the erythrocytes of the rabbit are most liable to haemolysis and those of the goat and rat show the greatest resistance when they are thrown into the solution. Generally speaking it seems probable, that less negatively charged erythrocytes in the NaCl solution are more liable to the haemolytic effect of the base, the case of the dog being excluded. 16. Those elements which possess lower solution pressures than hydrogen have generally a strong power to dissolve or destroy the erythrocytes, and less negatively charged erythrocytes seem to be more liable to haemolysis in solutions of the copper, mercury, silver, gold or platinum compounds. 17. Those elements which possess higher solution pressures than hydrogen have generally only a weak haemolytic effect or none at all, but the trivalent cations Fe(…) and Al(…) are powerful in causing haemolysis, their effect resembling that of the acid. 18. The haemolytic effect of saponin, natrium oleat and alcohol has no bearing on the electric charge of the erythrocytes and seems to be chiefly concerned with the action to dissolve the lipoid. 19. Likewise the haemolysis caused by hypotonic solutions has no relation to the electric charge of the erythrocytes.20. The resistance of the erythrocytes towards hypotonic NaCl solutions is increased by the effect of the alkali and decreased by that of the acid (HAMBURGER). This change is seen very markedly in the goat erythrocytes which have a strong negative potential, while the positively charged erythrocytes of the rabbit in such cases show very little or no change at all. 21. The haemolytic serum has a power to neutralize the charge of the erythrocytes. This action must be attributed to either the amboceptor or agglutinin, the complement having surely nothing to do with it. An experiment on the goat erythrocytes gave a result, which seems to suggest, that the amboceptor acts upon the erythrocytes more effectually than the agglutinin, as far as the electric charge is concerned.