428 BACTERIOLOGY. 



growing or dying. Represent the results graphically, 

 and it will be noticed that in many cases there is at 

 first, during the first three or four days, a multiplica- 

 tion, after which there is a rapid diminution ; and, if 

 the organism does not form spores, usually complete 

 death in from ten to twelve days. This is not true for 

 all organisms, but does hold for many. 



Where it is not convenient, however, to make the 

 analysis on the spot, the sample of water should be col- 

 lected and packed in ice and kept on ice until ready for 

 use, which should in all cases be as soon after its collec- 

 tion as possible. 



For the collection of water for this purpose, a con- 

 venient vessel to be employed is a glass bulb (Fig. 87) 

 or balloon, which one soon learns to make for oneself 

 from glass tubing. 



Fig. 87. 



Glass bulb for collecting samples of water. 



It consists simply of a round glass sphere blown on 

 the end of a glass tube, which latter is subsequently 

 drawn out into a fine capillary stem and sealed while 

 hot. As it cools, the contraction of the air within the 

 bulb results in the production of a negative pressure. 

 If the point of the stem be broken off under water, the 

 water is pressed up into the bulb, because of the existence 

 of the negative pressure within. The negative pressure 

 obtained in this way is frequently not sufficient to permit 

 of the bulb being completely filled, and often only a few 

 drops of fluid can be obtained. To obviate this the 



