and Laboratory Methods. 



1403 



With such an apparatus, ten first quality negatives, of any diameters from 

 4000 down, can easily be made in a couple of hours. They can be more easily 

 and certainly made than the same number of fair to middling negatives of from 

 40 to 100 diameters on any improvised outfit. 



Fig. 6. — Unsectioned blastula of ascaris. x 1500. 



This makes photomicrographs of all powers really usable. Previous to 

 1899, experts were happy with ten failures to one success ; one correct negative 

 had to pay for an entire evening's work. This made them expensive, too 

 expensive for any use, however cheap the apparatus. 



Earlham College. D. W. DennIS. 



Notes on Testing for B. Coli in Water 



Test for B. Coli in Large Volumes. 



In 1898 we published a description of the methods employed at the Lawrence 

 Experiment Station in the routine examination of water for B. coli. These tests 

 were all made in one cubic centimeter. 



The description of the preliminary test in large volumes, usually 100 cubic 

 centimeters, was omitted at this time, as the test was then in the experimental 

 stage. This test, as it is now made, has been in use in this laboratory for about 

 two years, and has proved very satisfactory. The water to be tested is collected 

 in clear, glass-stoppered bottles, of the tall Blake pattern, holding about eight 

 ounces, with a graduation mark for 100 cubic-centimeters. To 100 c. c. of the 

 water, in the bottle, we add 10 c. c. of a strong carbolated dextrose broth, which 

 is prepared as follows: 100 grams of dextrose and 50 grams of peptone are 

 dissolved in 1 liter of boiling water. After cooling, and filtering through paper 

 till clear, 50 c. c. of a 5 per cent, aqueous solution of phenol is added, or approxi- 

 mately 0.25 per cent, of phenol. The solution is now ready for use, and 

 requires no sterilizing. There is enough phenol present to prevent the spoiling 

 of the solution, especially if kept on ice, as we always do. 



