Of these different methods that of Pasteur has been most extensively adopted. The temperature of culture (42° C.) prevents the formation of spores and the duration of exposure to air gradually lessens the virulence until in 12 or 13 days it is not fatal to the Guinea pig and after 31 days it fails to kill the young mouse. Thus preparations of varying grades of virulence, and adapted to the varying susceptibility of different animals, are secured. The protective inoculation is made by preference in spring, when there is less chance of complication by a coincident accidental infection, it is to be avoided if possible in animals at hard work, in advanced gestation, in full milk, in extreme youth, or in ill health. To secure the best results it should be repeated with a stronger preparation 12 to 15 days after the first injection. The acquired immunity lasts a year and over, and it is probably perpetuated by new and non-fatal doses taken in casually, on the anthrax pastures. Hundreds of thousands of live stock in all parts of the world have been treated in this way with the result of reducing a mortality of two, five or ten per cent. to insignificant proportions. It can only be safely adopted on anthrax lands, as elsewhere it may lead to the stocking of new areas with a malignant germ which in young and susceptible animals reacquires its original virulence. It can never be safely ignored that we are dealing with the living seed of a most deadly infection. Though robbed of a large part of its virulence by artificial culture at 107:5° F., yet many accidental conditions, contribute to a relapse to its original potency, and when it has once killed a victim, the reacquired virulence is usually persistent. If the virus employed for protective purposes in cattle and sheep, is inoculated on Guinea pigs of 1 to 30 days old, from these on those of several months, and from these last on sheep, the virulence is constantly and persistently enhanced. The same is true of the microbe which is inoculated on a succession of pullets of steadily encreasing ages (Roux and Chamberland), or on a succession of pigeons (Metchnikoff). The germs reinforced in potency in any such way are liable to be the starting points for dangerous infections in animals and permanent contamination of soils and waters. Fortunately an occurrence of this kind is rare, yet with a wide application of the Pasteurian inoculation the opportunities also are great, and with the free sale and distribution of the mitigated virus (anthrax “vaccine”), the evil may grow indefinitely. The method departs from the ideal one, aimed at a final extinction of the disease, and accepts in place a mere temporary protection of the herd or flock, and though in this affection eradication cannot always be secured, every effort should be made to gain it and above all to prevent an encrease of the area of infection.