STRONG DRINK AND TOBACCO SMOKE. 69 



resembles, and, next with those previously illustrated. 1 

 think it will be difficult to find amongst natural objects 

 better examples of exquisite gradations of form and 

 structure than these wayside weeds do furnish. 



For the purpose of studying the forms and characters 

 of these hairs under the microscope, the epidermis, or 

 skin of the leaf is detached from the main rib of veins 

 on the under side of the leaf by gently cutting it with 

 a very sharp knife-blade, raising the edge of the skin 

 with a pair of delicate forceps, and peeling it off in a 

 lateral direction. Or, if the skin of the leaf-blade is 

 required, by making a slight incision at that point where 

 the blade joins a vein or midrib. The delicate mem- 

 brane thus obtained is carefully placed in water on a 

 glass slide covered with thin glass, and, if necessary, a 

 drop of caustic potash added to the water by means of 

 a glass rod to remove impurities. 



To examine the structure internally, a piece of it 

 is inserted between two pieces of cork ; these are then 

 placed face to face and inserted into the mouth of a 

 glass tube. After moistening the cork with water, thin, 

 transverse, vertical sections may be obtained by using 

 a very sharp razor, or, what is better, one of the fine 

 knives used by surgeons in delicate dissections and 

 operations on the eye. 



Sections thus obtained will resemble, according to 

 their thickness, the loosely aggregated cells of the 

 tobacco leaf (Plate 9, fig. 4), or those more compactly 

 arranged, as in the leaf of the hop. 



