Again, if the nutrient medium become acid in reaction their growth is checked, at least in gelatine and meat infusion; but singularly enough, they continue to grow on the surface of a boiled potato which has become acid, showing that all acids are not equally obnoxious to them.  But here, as with other substances which hinder their growth, they do not kill the bacilli.  Davaine has shown that iodine is a strong bactericide.  He experimented with anthrax bacilli in water to which iodine was added, and the bacilli were destroyed.  But practically the organisms have to be dealt with in the alkaline contents of the bowel, or in the blood or fluids of the tissues, where iodine cannot remain in the free state.  Koch found that the addition of an aqueous solution of iodine (1 in 4,000) to meat infusion, in the proportion of 1 in 10, did not in the least interfere with the growth of the bacilli in that medium.  He did not pursue this line of inquiry, seeing that in practice larger quantities of iodine than that could not be given.  Alcohol first checks the development of the comma bacilli when it is mixed with the nutrient fluid in the proportion of 1 in 10, a degree of concentration which renders it impracticable for treatment.  Common salt was added to the extent of 2 per cent. without influencing the growth of the bacilli.  Sulphate of iron, in the proportion of 2 per cent., checks this growth, probably by precipitating albumimites from the fluids, and possibly also by its acid reaction; certainly it does not seem to have any specific disinfecting action—­i.e., in destroying the bacilli.  Indeed, Koch thinks that the admixture of sulphate of iron with faecal matter may arrest putrefaction, and really remove what may be the most destructive process to the comma bacilli.  Hence he would distinguish between substances which merely arrest putrefaction and those which are bactericidal; for the former may simply serve the purpose of preserving the infective virus.  Among other substances which prevent the growth of the comma bacilli may be mentioned alum, in solutions of the strength of 1 in 100; camphor, 1 in 300; carbolic acid, 1 in 400; oil of peppermint, 1 in 2,000; sulphate of copper, 1 in 2,500 (a remedy much employed, but how much would really be needed merely to hinder the growth of the bacilli in the intestine!); quinine, 1 in 5,000; and sublimate, 1 in 100,000.  In contrast with the foregoing measures for preventing the growth of these bacilli is the striking fact that they are readily killed by drying.  This fact is proved by merely drying a small drop of material containing the bacilli on a cover-glass, and then placing this over some of the fluid on a glass slide.  With anthrax bacilli vitality is retained for nearly a week; whereas, the comma bacillus appears to be killed in a very short time.  Thus it was found that although vitality was retained—­depending largely upon the number of bacilli—­for a short time, yet withdrawal of the nutrient fluid for