Another peculiarity was the slowness with which the gelatine liquefied, and the narrow limits of this liquefaction in the case of a gelatine disk.  Cultures of the comma bacillus were also made in agar-agar jelly, which is not liquefied by them.  On potato these bacilli grow like those of glanders, forming a grayish-brown layer on the surface.  The comma bacilli thrive best at temperatures between 30 deg. and 40 deg.  C., but they are not very sensitive to low temperatures, their growth not being prevented until 17 deg. or 16 deg.  C. is reached.  In this respect they agree with anthrax bacilli.  Koch made an experiment to ascertain whether a very low temperature not merely checked development but killed them, and subjected the comma bacilli to a temperature of 10 deg.  C. They were then completely frozen, but yet retained vitality, growing in gelatine afterward.  Other experiments, by excluding air from the gelatine cultures, or placing them under an exhausted bell jar, or in an atmosphere of carbonic acid, went to prove that they required air and oxygen for their growth; but the deprivation did not kill them, since on removing them from these conditions they again began to grow.

The growth of these bacilli is exceptionally rapid, quickly attaining its height, and after a brief stationary period as quickly terminating.  The dying bacilli lose their shape, sometimes appearing shriveled, sometimes swollen, and then staining very slightly or not at all.  The special features of their vegetation are best seen when substances which also contain other forms of bacteria are taken—­e. g., the intestinal contents or choleraic evacuations mixed with moistened earth or linen and kept damp.  The comma bacilli in these conditions multiply with great rapidity so as to far outnumber the other forms of bacteria, which at first might have been in far greater abundance.  This state of affairs does not last long; in two or three days the comma bacilli began to die off, and the other bacteria began to multiply.  Precisely the same thing takes place in the intestine, where, after the rapid initial vegetation is over, and when exudation of blood occurs in the bowel, the comma bacilli disappear and putrefactive bacteria predominate.  Whether the occurrence of putrefaction is inimical to the comma bacilli has not been proved, but from analogy it is very probable.  At any rate, it is important to know this for certain, for if it be so, then the comma bacilli will not thrive in a cesspit, and then further disinfection would be unnecessary.  These bacilli thrive best in fluids containing a certain amount of nutriment.  Experiments have not yet shown the limits in this respect, but Koch has found them capable of growing in meat broth diluted ten times.