819 it out over as large a surface as possible on the agar plate. Repeat this with the other dilutions when their 15 minutes' incubation is up, and with the second series after an hour has elapsed. Incubate the plates ; growth is complete in 24 hours, but the results can be read off before then. I append some of my results :-The expression does not kill " may be taken in most cases as implying that it causes a diminution in the number of organisms, but does not effect actual sterilisation ;

more »

... dilution, therefore, may be taken as a convenient end-point if various antiseptics have to be compared. For instance, there is a tradition that eusol and Dakin's solution are several times more powerful than carbolic acid, whereas, as a matter of fact, it is seen when this method of testing is used that these substances undiluted (0' 5) are about equal in effect to a 1 in 70 dilution of carbolic-in other words, carbolic acid is 70 times as strong. But this is only if they are tested at the end of a quarter of an hour ; if tested at the end of one hour the chlorine preparations appear to be quite inert, the surviving bacteria having grown until, unless special methods of plating are used, they appear as abundant as in the controls. To demonstrate complete killing with eusol it is necessary to have approximately two volumes of the antiseptic to one of blood. The killing point of iodine is not given. It is about 1 in 60, but at a dilution like this the blood is turned into a thick pasty mass, very unsuited for accurate work. -Iodine is sometimes used in a dilution of 1 in 300 or 400 to sterilise " wounds. Such a dilution is quite inert. The results with malachite green may excite surprise ; it is by far the most powerful antiseptic that I have investigated. Unfortunately its action on the living cells is even more powerful, otherwise it would be the ideal antiseptic for surgical use.