274 



BACTERIOLOGICAL METHODS 



(0.9 per cent.) and a suspension of 5 per cent, defibrinated ox 

 blood in 0.9 per cent, salt solution. 



To make the experiments test-tubes are used and the compound 

 microscope is not required. In a series of standard test-tubes 

 place 2.5 cc. of the suspended blood (in the sodium chloride solu- 

 tion) and the same amount of the solution to be tested (in varying 

 amounts of physiological salt solutions, therefore different strength 

 solutions) in order to ascertain the exact point when hemolysis 

 takes place. A solution which does not produce hemolysis after 

 a definite period of time (3 hr.), but which does result in hemolysis 

 on the smallest further addition of the substance under examina- 

 tion is spoken of as a "critical solution." The time limit in these 

 tests is 3 hr. If after the expiration of this period of time, the trace 

 addition of the solution does not produce the hemolytic effect, 

 the test is negative and the next stronger or higher concentrate 

 must be tried. The term critical coefficient refers to the number 

 giving the concentration of the substance necessary to hemolyze or 

 kill the red corpuscles. 



The following is the result obtained by Vandevelde regarding 

 the critical solution of ethyl alcohol. 



From this table it will appear that the critical solution of ethyl 

 alcohol contains 19.5 cc. of absolute alcohol in 100 cc, or 15.489 

 grams of alcohol in 100 cc. According to Vandevelde, the addi- 

 tion of methyl alcohol diminished the toxicity of ethyl_^alcohol, 

 whereas the higher alcohols were found to be more toxic than the 



