=Nature of the Toxins.=--The molecules of the toxins are very nearly like those of the diastases. Like these, the toxins appear to have a very complex, and very unstable, internal structure. Their mode of action frequently depends, as in the case of the diastases, upon the medium in which they occur. Again, like the diastases, they are generally destroyed by the action of sufficiently prolonged heat, but less easily, for there are certain toxins that resist a temperature of 100° C. for an indefinite period. They are, like the diastatic albuminoids, insoluble in strong alcohol, and are precipitated from their solutions on the addition of this reagent. They easily adhere to precipitates that form in liquids in which they occur in solution, and possess the remarkable property of diastases in that imponderable masses produce considerable results.[28] [28] See POZZI-ESCOT: Les diastases et leurs applications, published by Masson, 1900; and _Traité de Physico-chimie_. Although closely allied to certain alkaloidal bases, the toxins are sharply distinguished by the remarkable fact that their action is never immediate, but is always preceded by a period of incubation, which may be quite long. Like the alkaloidal bases, they appear to result from the hydrolyzing breaking down of albuminoids and nucleo-albumins, and they appear to be intermediary, from a chemical point of view, between these bodies, the general characters of which they retain, and the alkaloids proper, or ptomaines, to which we have called attention, and the principal chemical and physiological properties of which they possess. No absolutely precise knowledge is had regarding the chemical nature and constitution of these remarkable substances. A number of analyses of these substances have been published which, in general, permit no definite conclusion to be drawn.[29] I have, however, elaborated several speculative ideas regarding this subject.[30] [29] Regarding this see the works by KOCH and BRIEGER, _Deutsche Medicin. Wochenschr._, Oct. 22, 1891. [30] POZZI-ESCOT: Nature des Diastases. Published by J. Rousset, Paris, 1903. See also Recherches de la Nature Chimique des Diastases Oxydantes. _Revue génér. de chimie_, VII, pp. 129-136; and Aperçus sur la nature chimique des Diastases, _Bulletin de l'Association de Chimistes_, 1904, p. 769.--Propriétés Catalytiques de Quelques Diastases; _Ibid._, 1904, p. 1247. We must here call particular attention to the ideas of Ehrlich regarding the constitution of the toxins. According to this scientist, their molecules contain two functional groups; the one, to which he has given the name "haptophore," is that which enables the toxin to attach itself to any cellular element whatever, and which it then renders non-toxic by means of the other, or "toxophore," group. We will particularize farther on regarding this very important conception.