616 APPLICATION OF METHODS OF BACTERIOLOGY 



Note. — Inoculate a tube containing about ten cubic 

 centimeters of sterilized distilled or tap water with a very 

 small quantity of a solid culture of some one of the organ- 

 isms with which you have been working, taking care that 

 none of the culture-medium is introduced into the water- 

 tube and that the bacteria are evenly distributed through 

 it. Make plates at once from this tube, and on each suc- 

 ceeding day determine by counts whether there is an increase 

 or diminution in the number of organisms — i. e., if they are 

 growing or dying. Represent the results graphically, and 

 it will be noticed that in many cases there is during the 

 first three or four days a multiplication, after which there 

 is a rapid diminution; and, if the organism does not form 

 spores, usually 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 taken and packed 

 in ice and kept on ice until the plates can be made from it, 

 which should in all cases be as soon after its collection as 

 possible. 



For the collection of samples from the deeper portions 

 of streams, lakes, etc., a number of convenient devices have 

 been made. A very satisfactory apparatus has been made 

 for me by Messrs. Charles Lentz & Sons, of Philadelphia. 

 It consists of a metal frame-work, in which is encased a 

 bottle provided with a ground-glass stopper. To the stopper 

 a spring clamp is attached, and this in turn is operated by 

 a string, so that when the weighted apparatus is allowed to 

 sink into the stream the stopper may be removed from the 

 bottle at any depth by simply pulling upon the string. 

 When the bottle is filled with water the stopper is allowed 

 ■ to spring back into position by releasing the string. The 



