VII PRACTICAL DIRECTIONS 123 



To another drop of blood add distilled water. The corpuscles be- 

 come swollen up and partly dissolved, and the colouring matter 

 (hcetiioglohin) of the red corpuscles is dissolved out into the plasma. 



Examine some coagulated blood under the microscope, and note the 

 threads of fibrin in which the red corpuscles are entangled, and the 

 serti?}i. 



Examine once more the circulation in the web (p. 103), using the high 

 power, and follow the course of both red and colourless corpuscles 

 through the vessels and capillaries. By focussing to the surface of the 

 web the flattened epithelial cells of the epidermis or outer skin can be 

 seen, and at a deeper level the black pigment cells (see p. 128, and 

 compare Figs. 24 and 27). 



2. Columnar epithelium. — Take a small piece of frog's intestine, 

 and place it for 24 hours in a mixture called Ranvier's alcohol, consisting 

 of one part of methylated spirit and two parts of water. With fine 

 scissors snip off a very small piece — not larger than a pin's head — from 

 the inner surface of the mucous membrane, place it on a slide in a drop 

 of water, and with two dissecting needles tease it out by tearing it into 

 the smallest possible particles. The operation is best done under a lens. 

 Then put on a cover-glass, and examine first with the low and then with 

 the high power. (Remember that a cover-glass must always be used 

 with the high power. ) 



Note the minute, more or less conical cells of columnai epithelium 

 (Fig. 28), each containing a nucleus. Observe the goblet-cells amongst 

 the ordinary columnar cells. Stain with magenta, which is more effective 

 than methyl-green in specimens previously treated with alcohol, and 

 wash with water. (Salt-solution need only be employed in the case of 

 fresh or living tissues.) Sketch. 



3- Ciliated epithelium- — Snip off a very small bit of mucous 

 membrane from the mouth of a recently killed frog, and tease it out in 

 salt-solution (Fig. 29). 



Note the form of the cells and their nuclei : they are relatively 

 shorter than the columnar cells just examined, and each bears a number 

 of delicate vibratile cilia at its free end. Observe the movements of 

 the cilia. Sketch. 



Treat with methyl-green, magenta, or acetic acid, when the nucleus 

 will become more apparent. 



Perforn) experiment described on p. i IQ to show the action of the cilia 

 ^s a whole in the entire aninial. 



