GENERAL PRINCIPLES 165 



resistant to injury by heat, light, drying, and chemicals. 

 True spores or endospores are to be distinguished from 

 arthrospores, the existence of which is now seriously 

 questioned. An arthrospore is a bacterium which enters 

 into a resting stage without any new formation within 

 the protoplasm. It stains well with ordinary stains, and 

 has no distinct capsule, but is stated to have increased 

 resistance to external agents. A true spore (i) resists the 

 ordinary staining method ; and (2) shows very great 

 resistance to destruction to the usual agents. 



Flagella Staining. Flagella are hair-like organs 

 used for locomotion, and have been described as occurring 

 on bacilli, spirilla, and a few species of cocci. They are 

 best seen in young cultures, 10 to 18 hours old, at 37 C. 

 McCrorie's method gives admirable results when the 

 technique is carefully followed. 



McCrorie's Flagella Stain. Measure out and mix : 

 Night-blue, 1 grm. in 20 c.c. of absolute alcohol ; potash 

 alum, 1 grm. in 20 c.c. of distilled water ; tannin, 1 grm. 

 in 20 c.c. of distilled water. Allow mixture to stand for 

 twenty-four hours, and filter supernatant fluid. Keep 

 stain in incubator and filter again when using. 



Method. 



(1) Take some distilled water at 37 C. in a watch- 



glass ; place therein a loopful of young agar cul- 

 ture, and allow to swim off and diffuse without 

 stirring. 



(2) Take several loopfuls of this solution, and deposit 



them singly, without smearing, on a clean cover- 

 slip. 



(3) Dry in the incubator at 37 C. 



(4) Apply stain (also at 37 C.) and replace in incubator 



for 10 minutes. 



(5) Wash off stain by dipping cover-slip edgeways 



several times into water at 37 C. 



(6) Dry in the incubator. 



(7) Mount : or counterstain bodies with strong fuchsin 



solution for 2 minutes ; wash, and dry as 

 before ; mount. 

 Flagella are blue, bacillary bodies are red. 



