The Microscope. 219- 



ABSTRACTS. 



THE BIOLOGICAL ANALYSIS OF AVATEE. 



In his article on Bacteria in Ice in the Medical Record of March 

 28, Dr. T. Mitchell Prndden, gives the following method for the 

 biological analysis of water : 



In the first place, all the vessels and instruments which will 

 come in contact with ovir water, and the food which we prepare for 

 the nourishment of the bacteria are completely freed from all living 

 germs, which are almost omnipresent in the air and on the things we 

 touch. This is usually done by prolonged heating or steaming. 

 Thus freed from all living things, no matter how small, our materials 

 are said to be sterilized. The food which we prepare for the bacteria 

 in water-analysis is usually beef -tea, with a little peptone and common 

 salt and enough gelatin to make it moderately solid when cold. 

 This is called the nutrient gelatin, or culture -medium and it is 

 poui'ed into test-tubes — a few teaspoonfuls in each. In this medi- 

 um most of the bacteria which are commonly found in water will 

 readily grow. It is clear and transparent and usually slightly 

 yellowish in color. Now, one of the prominent characteristics of 

 these lowly organisms, the bacteria, is their capacity under favorable 

 conditions of nutriment and temperature, of rapid and enormous 

 increase in numbers. This occurs by the slight enlargement of the 

 individual bacteria apd their division across the middle into two. 

 These two then each again divide, and so on until within a shoi't 

 time an almost innumerable number of new individuals are produced 

 from the original germ, each one the exact counterpart of its an- 

 cestors. 



It is estimated that if the conditions are favorable, a single bac- 

 terium, by this process of growth and subdivision, may give rise to 

 more than sixteen and a half millions of similar organism within 

 twenty-four hours. But so minute are most of these that at an aver- 

 age estimate the whole of these sixteen and a half millions would 

 occupy a space less than the sixteen- hundredth of a cubic inch. When 

 a water analysis is to be made, the nutrient gelatin in one of the 

 tubes is melted by gentle heat and thoroughly mixed by shaking with 

 a measured quality of the water to be examined. In this way the 

 bacteria contained in the water, always an unknown quantity and of 

 course quite invisible, are evenly distributed through the gelatin. 

 To insure accuracy, duplicate analyses are always made. The quan- 

 tity of water used is usually one cubic centimetre, and this is taken 



