It is believed by Delezenne that the explanation of this phenomenon may be that the doses, which are weak but sufficient to produce the disintegration of the leucocytes, injure the red corpuscle in only a slight degree, while the stronger doses are equally destructive to the two kinds of blood corpuscles. It follows that we must understand that there are two phases in the action of venoms: one _negative_, when the dose absorbed does not injure the leucocytes; the other _positive_, when the leucocytes are destroyed. If the blood of the dog remains non-coagulable when mixed with doses of venom which, on the contrary, are actively coagulant for the blood of the rabbit, the reason would be that the leucocytes of these animals are not equally resistant to venom. This conception, however, does not conform to the facts that I have myself observed. I have always found that viper-venom, mixed with citrate- or oxalate-plasma of the dog, rabbit, or horse, coagulates these various plasmas when the venom is in weak doses, while with strong doses coagulation is not produced. To be quite accurate, it should be stated that the quantity of venom necessary to render the plasma of the dog, or of the horse, non-coagulable is less than that which must be employed in the case of the plasma of the rabbit. I have caused Noc to take up anew the study of this question in my laboratory, with venoms of nine different origins, and I here give a _résumé_ of the results of his researches.[37] I. COAGULANT VENOMS. The venoms of VIPERIDÆ studied range themselves as follows according to their coagulant power:-- CROTALINÆ: _Lachesis lanceolatus_ (Fer-de-lance, Martinique). _Lachesis neuwiedii_ (Urutù, Brazil). _Lachesis mutus_ (Bushmaster, or Surucucu, Brazil). _Lachesis flavoviridis_ (Japan). VIPERINÆ: _Vipera russellii_ (Daboia, India). The venoms of _Ancistrodon contortrix_ and _A. piscivorus_ (CROTALINÆ) proved entirely inactive. No COLUBRINE venom exhibited coagulant power, whatever the dose employed. There is, therefore, a very decided difference between venoms of divers origins as regards their effects upon the coagulation of the blood.