276 BACTERIA. 



by immersing them for some time in i ,000 parts of nutrient 

 fluid, to which one part of carbolic acid had been added. 

 Under these circumstances the growth of the organism is 

 not completely prevented, but no spores appear to be de- 

 veloped. It cannot multiply at a temperature below 16 C. 

 nor above 45 C., 30 to 37 C. being the optimum tempera- 

 ture. It is distinctly aerobic in its growth, and cannot 

 develop unless it can obtain a pretty free supply of oxygen. 



It has already been stated that the organisms which occur in 

 the blood are homogeneous, and it is a well-known fact that 

 spores are never developed in the bacillus that grows in the 

 blood, the multiplication there being entirely vegetative in 

 character, and being due to fission or division of the rods as 

 they increase in length. The same thing holds good even in 

 the dead body so long as it remains intact ; when once, how- 

 ever, the blood is allowed to come to the surface and in con- 

 tact with oxygen, spores are very rapidly formed within the 

 bacilli. This spore formation will not take place below from 

 24 to 26 C. (Koch says 18 C.), and then only in the 

 presence of oxygen, so that they can best be seen in those 

 bacilli that are cultivated on the surface of such nutrient 

 substrata as agar-agar, solidified blood serum, and potato, or 

 in fluid media through which a pretty constant stream of 

 oxygen is allowed to pass. 



In this respect the spore formation of anthrax bacilli ap- 

 pears to agree with the sporulation of yeasts, which, it will be 

 remembered, takes place best on a surface of plaster of Paris 

 that is constantly kept moist and well supplied with air. 



Anthrax bacilli as distinguished from the spores are very 

 readily killed. The ordinary putrefactive processes that 

 are undergone in the decomposition of carcases in which 

 these organisms have been present during life, especially if 

 the air be excluded, cause the death of these bacilli in about 

 a week. The temperature of boiling water maintained for a 

 few seconds kills the bacilli, but, according to Klein, boiling 

 for ten minutes is not to be relied upon to kill the spores 

 although Koch states that at 100 C. the spores are killed in 

 five minutes. The bacilli are killed by a two minutes' ex- 

 posure to a one per cent, solution of carbolic acid in water, 

 whilst the spores may remain alive for more than a week in 

 a similar solution. They must be kept for nearly a week in 

 a three per cent, solution, and twenty-four days in a five per 



