In view of the frequent persistence of this malady in a given stable for a great length of time, successive animals being attacked at long intervals, and where isolation was impracticable, Beckmann rubbed the nasal discharges of the sick on the nasal mucosa of the unaffected, producing the disease almost invariably in a mild form. The infected animals were placed in the best hygienic conditions, the duration of the infection was shortened, and the horses being rendered immune, the stable was then disinfected with a satisfactory result. Schütz, Hill, Pilz and a number of others have sought artificial immunity, by the injection of blood serum from a horse that has recently recovered from the malady. The results were very contradictory. In some cases the disease came to a sudden end. In other stables no new cases appeared either in those treated with serum or in those left without treatment. In other experiments, new cases occurred among those treated with the serum;—in Weishaupt’s cases after a lapse of one or two months. This is exactly what might be expected. If the horse supplying the blood serum had really recovered, and if the microbes (streptococci) had disappeared from the blood, the latter would of necessity retain little of the toxins, but much more of the antitoxins, the active production of which would be continued by the stimulated leucocytes. These antitoxins would neutralize the toxins, in case of invasion and prevent that from reaching the maximum of intensity that it would otherwise have reached, but would be powerless to stimulate the leucocytes of the inoculated animal into the habit of themselves producing antitoxins. This would act rather as a curative than a prophylactic agent, and its value would be spent as soon as the injected antitoxins were eliminated from the system. The true line of inquiry would have been, whether injection of the toxins, which acting on the leucocytes would have stimulated these to the habit of producing antitoxins in large amount, might not be expected to give an immunity as lasting as that which follows on a casual attack of the disease. Lignieres appears to have approximated to this, in his experiments on mice and rabbits. In horses suffering from contagious pneumonia it lowered the temperature, but did not materially affect the result of the attack. If we adhere to Lignieres’ own theory of causation by cocco-bacillus and later by streptococcus or some other complicating infection, we can scarcely hope that the toxins of the streptococcus or other complicating microbe will immunize against the cocco-bacillus or mutually against each other. If complete protection is aimed at, the toxins of his cocco-bacillus, and of Schütz’s streptococcus, and of any other possible microbe which may produce a secondary complication, ought to be employed. At the date of this writing no satisfactory sero-therapy for this disease has been worked out and publicly demonstrated.