176 BACTERIOLOGY. 



and how much of either is required. In general, it may 

 be said that bacteria which produce acids in the media 

 in which they are growing require the addition of alka- 

 lies to the mordant, while those that produce alkalies 

 require acids to be added. By following LofJfler's direc- 

 tions the delicate, hair-like flagella on motile organisms 

 may be rendered plainly visible. 



There are several points and slight modifications in 

 connection with this method that require to be empha- 

 sized in order to insure success : the culture to be em- 

 ployed should be young, not over 18-20 hours old ; it 

 should have developed for this time on fresh agar-agar 

 at 37° to 38° C. ; the mordant should not be perfectly 

 fresh, as the best results are obtained from the use of 

 old solutions that have stood exposed to the air and 

 that have been filtered just before using ; when placed 

 on the cover-slip and held over the flame never heat the 

 mordant to the boiling-point ; indeed, the best results are 

 obtained when the preparation is held high above the flame 

 and removed from it at the first evidence of vaporization, 

 or, better still, a little before this point is reached. We 

 have derived no advantage from the addition of acids 

 or alkalies to the mordant, as recommended by Loffler ; 

 but obtain, with a fair degree of regularity, satisfactory 

 results through the use of the neutral mordant alone.' 



Btjjstge's Method. — A useful modification of Lof- 

 fler's method is that recommended by Bunge : prepare 

 a saturated solution of tannin, and a solution of liquor 

 ferri sesquichlor. of the strength of 1 : 20 of distilled 

 water. To 3 parts of the tannin solution add 1 part of 



• I am indebted to Dr. James Homer Wright, Thomas Scott Fellow 

 in Hygiene, 1892-93, University of Pennsylvania, for some of the 

 suggestions in connection with the modification of this method. 



