THERMAL DEATH-POINT OF BACTERIA. 



67 



some such form of locomotive apparatus, because similar 

 appendages had been seen upon some of the large motile 

 spirilla found in stagnant water, but it was not until a 

 few years ago that the accuracy of this assumption was 

 actually demonstrated. By a special method of staining 

 Loffler 1 was the first to render visible these hair-like 

 appendages. His method, as well as the several modi- 

 fications that have been made of it, depends for success 

 upon the use of mordants, through the agency of which 

 the stains employed are caused to adhere with increased 

 tenacity to the objects under treatment. 



FIG. 7. 



a b c 



a. Spiral forms with a flagellum at only one end. 6. Bacillus of typhoid 

 fever with flagella given off from all sides, c. Large spirals from stagnant 

 water with wisps of flagella at their ends (spirillum undula). 



THERMAL DEATH-POINT OF BACTERIA. By " ther- 

 mal death-point of bacteria " is meant the temperature 

 necessary to kill them in a given time. As this varies 

 with different species, it is an aid to identification. For 

 the practical purposes of the sanitarian the knowledge is 

 of fundamental importance. The thermal death-point of 

 an organism is ascertained by subjecting it to varying de- 

 grees of temperature for five or ten minutes until the point 



1 Loffler's method of staining will be found iu the chapter devoted 

 to this part of the technique. 



