1.] THE HISTORY OF THE COMMA-BACILLUS. 13 



trifle, about two millimetres, under the mica plate, up to 

 which point the air has been able to force its way. But 

 under the mica-plate itself nothing grows. Extremely small 

 colonies, invisible to the naked eye, do, it is true, appear, 

 which probably owe their origin to the oxygen existing in 

 the gelatine, but they do not increase in size afterwards. 

 An experiment was made in another mariner. Little glasses 

 containing nutritive gelatine, which had been inoculated 

 with comma-bacilli, were placed under an air-pump, and 

 others prepared in the same manner were kept outside the 

 air-pump. It was then seen that those under the air-pump 

 did not grow, but only those outside it. But when those 

 that had been under the air-pump were again placed in the 

 air, they began to grow. Hence they had not died ; they 

 only wanted the necessary oxygen to be able to grow. 

 The same occurs when the cultivations are brought into 

 an atmosphere of carbonic acid. Whilst the cultivations 

 that have been kept for comparison outside the carbonic 

 acid atmosphere grow in the usual manner, those that are 

 in a stream of carbonic acid remain undeveloped. But 

 in this case, also, they do not die ; for, after having been 

 for some time in the carbonic acid, they begin to grow 

 immediately after they have come out of it. 



" On the whole, comma-bacilli, as I have repeatedly 

 observed, grow extremely rapidly. Their vegetation very 

 speedily reaches a maximum, at which it only remains 

 stationary for a short time, then diminishes again very 

 speedily. The comma-bacilli, when wasting away, lose 

 their shape ; they appear at one time shrivelled, and at 

 another time swollen, and in this state they are not at all, 

 or only slightly, susceptible to colour. The peculiar con- 

 ditions of vegetation of comma-bacilli can be best observed 

 by bringing substances which are rich in comma-bacilli, but 



