On experimenting with _washed_ corpuscles, it is found that venom alone is incapable of dissolving them. In order that dissolution may take place, we are obliged to add to the mixture either a small quantity of normal horse-serum, preferably _heated_, and, consequently, deprived of alexin (Calmette), or ½ c.c. of a 1 in 10,000 solution of _lecithin_ in physiological saline water (P. Kyes). Venom, therefore, is capable of hæmolysing red corpuscles only when it is _quickened_, either by heated normal serum, or by lecithin. The solution of lecithin employed for this purpose should be prepared by dissolving 1 gramme of lecithin in 100 grammes of pure methylic alcohol. Taking 1 c.c. of this dilution we add it to 9 c.c. of 8 in 1,000 saline solution, and make a second dilution of 1 c.c. of the foregoing mixture in 9 c.c. of saline water. This latter dilution of 1 in 10,000 is utilised as the reagent. Let us now see how the serum or lecithin acts. It has been shown by P. Kyes that with either of these substances the mechanism of the hæmolytic action is the same, for the serum quickens the venom only through the agency of the free lecithin it contains. The lecithin takes part in the reaction by combining with the venom to form a hæmolysing _lecithide_ more resistant to heat than its two components, for it may be heated for several hours at a temperature of 100° C., without the loss of any of its properties. When venom is brought into contact with certain kinds of highly sensitive red corpuscles, those of the rat for example, these corpuscles, although washed and freed from serum, may undergo hæmolysis. This result is due to the fact that these corpuscles contain sufficient quantities of lecithin, which becomes liberated from their protoplasm and, uniting with the venom, constitutes the active _lecithide_. It was already known that lecithin is capable of combining with various albuminoid matters and with sugars to form _lecithides_. We must not, therefore, be surprised to find that such a combination may take place with the proteic substances in venom. The combination in this case is a truly chemical one. Lecithin in its natural state, or that which is normally found in serums which quicken venom, such as horse-serum, even when heated to 65° C., therefore plays the part of _complement_ according to Ehrlich’s theory, or that of _alexin_ according to the theory of Bordet, while venom itself would be an _amboceptor_ or _sensitiser_.