1894 THE MICROSCOPE. 3 



The disc of Ophiocoma can be bleached readily by 

 immersion in caustic potash, but care must be taken not 

 to go so far as to dissolve the integuments. 



I VIII. — SCALARIFORM DUCTS. 



The stem of a fern is often of a deep brown color, very 

 strong and hard. It owes these properties to a series of 

 cells having very hard tissue called sclerenchyme. Within 

 are series of bundles of Scalariform ducts (tracheides). 

 They are so called from their presenting a regular ladder- 

 like appearance {scala, a ladder). A thin section cut 

 obliquely across the stem displays very well the beauti- 

 ful structure of these ducts. 



In the illustration (taken from the International Jour. 

 Mici^scopy), Fig. 1 shows a bundle of Scalariform ducts 

 taken from thft British " bracken " {Pterls aqmlina). 

 It is enlarged 20 diameters. Fig. 2 shows a large duct en- 

 larged 250 dia. and shows numerous elongated pores. 

 Fig. 3 shows a duct w^ith shorter pores. In Fig. 4 you 

 can see the ladder well defined (250 dia). Fig. 5 is de- 

 signed especially to show the thickness of the walls, and 

 the projection of the so-called bars (250 dia). Fig. 6 is 

 an end view of the bundle shown in Fig. 1. The ducts 

 being cut across are seen to be firmly embedded in pleu- 

 renchymatous tissue. 



Those wishing objects to use with their microscopes 

 illustrative of Scalariform vessels, can send for ^N'os., 27, 

 28. 29 or 30 of White's objects. The four can be had for 

 30 cents in stamps. 



The Typhus Bacillus. — Dr Fraenckel of Berlin, announces 

 that he has discovered a typhus bacillus ; and that by using it 

 in vaccination, he has produced a rapid, benign course of the 

 fever. Dr. Rumpf has cultivated aa anti-fever bacillus which, 

 he says, will cure typhus in eight days. 



