1886.] On the Multiplication of Micro-organisms. 



527 



Number of micro-organisms 

 Number of hours. obtained frcm 1 c.c. of water. 



1,073 



6 6,028 



24 7,262 



48 48,100 



These numbers represent the number of micro-organisms found in 

 the upper layers of the water without agitating the contents of the 

 bottle. More recently -this subject has been touched upon by Dr. T. 

 Leone (" Gazzetta Chimica Italiana," xv, 385), who found that the 

 micro-organisms present in the water supplied, to the city of Munich 

 became multiplied in the course of five days from 5 per cubic centimetre 

 to upwards of half a million in the same volume of water. 



As this subject is one which is of much importance, from many 

 points of view, I have carried out a number of experiments with the 

 object of throwing some light upon these phenomena. 



Methods of Experiment. 



The number of micro-organisms present in the liquids employed 

 was determined by means of Koch's method of plate cultivation with 

 gelatine peptone. The apparatus used was substantially the same as 

 that described in my previous paper (loc. c££.), a few modifications of 

 the process having, however, beeu since then introduced. The 

 sterile plates are now placed upon a levelled glass slab, resting upon 

 a dish containing iced water, and covered with a glass shade, the 

 latter being .momentarily raised whilst the inoculated and fluid gela- 

 tine is poured upon the plate. With this arrangement the solidifica- 

 tion of the gelatine is almost instantaneous, and the plate can be at 

 once transferred to the moist chamber for incubation, thus enabling 

 the preparation of a very much larger number of plates in a given 

 time than was. formerly possible, when the rate of solidification of the 

 gelatine was dependent upon the temperature of the room. Instead 

 of a solution of mercuric chloride in the moist chamber, I now simply 

 employ sterilised distilled water,, as I have found that the presence of 

 the mercuric chloride in the moist chamber may exercise a prejudicial 

 effect upon the full development of the colonies on the plate. When 

 these modifications of the process are carried out with care in a room 

 in which the distribution of dust is scrupulously avoided, the aerial 

 contamination is altogether insignificant, but the process should in all 

 cases be checked by pouring blank plates, in order to ascertain whether 

 the precautions employed have been adequate or not. When, however, 

 sufficient experience has been acquired in the management of the 

 process, the preparation of these blank plates becomes rather a matter 

 of form than of any practical importance, nevertheless when mixtures 



