A wide range of difference is exhibited by the various venoms, as regards their hæmolysing power in the presence of normal heated serum or lecithin. The venom of _Naja_ and that of _Bungarus_ are the most active. The action of the venoms of VIPERIDÆ, and especially of those of _Crotalus_, is very weak. For example, while 1 milligramme of _Cobra_-venom dissolves in from five to ten minutes 1 c.c. of a 5 per cent. dilution of red corpuscles in the presence of lecithin or normal heated serum, the same dose of the venom of _Vipera russellii_ takes thirty minutes to effect the dissolution, and the venom of _Lachesis lanceolatus_ takes three hours. P. Kyes and H. Sachs have discovered the apparently paradoxical fact that, if to the red corpuscles of certain species of animals _Cobra_-venom be added in increasing doses, hæmolysis augments up to a certain point, beyond which the destruction of the corpuscles shows progressive diminution. In a large dose _Cobra_-venom no longer produces any effect upon the corpuscles of the horse, for example, even when the venom is added in presence of a great excess of lecithin or heated serum. It would seem, then, that, according to the theory of Ehrlich, under the influence of an exaggerated amount of venom-amboceptor there is produced a deviation on the part of the complement (serum or lecithin), and that the latter, instead of fixing itself upon the corpuscles, becomes united with the surplus fraction of the amboceptors, which has remained free in the liquid. Noguchi,[51] resuming the study of this extremely curious action of strong doses of venom, observed that the red corpuscles of certain species of animals (such as the horse for example), when previously washed and held in suspension in a physiological solution of sea-salt containing 4 per cent. of _Cobra_-venom, acquire a considerable augmentation of resisting power with regard to various physical and chemical agents. In consequence of this they are no longer hæmolysed by distilled water, ether, or saponin. Nevertheless, acids or alkalies, except ammonia, destroy corpuscles treated with venom more easily than those in their normal condition. If corpuscles, previously treated with a strong dose of venom, are subjected to repeated washings in physiological saline solution, the special resistance acquired by them in the presence of the venom disappears; they even become more sensitive to the action of destructive agents, such as water, ether, or saponin. The principle contained in venom, to which must be attributed the protective action, is not destroyed by heating to 95° C., although at this temperature _Cobra_-venom becomes partially coagulated. Moreover, the protective substance is contained in the coagulum, while the _hæmolysin_ remains entirely in the filtrate. The agglutinin of venom, on the other hand, is destroyed at a temperature of 75° C. The protective substance, therefore, can be identified neither with the hæmolysin nor with the agglutinin.