vii PRACTICAL DIRECTIONS 123 



puscle becomes transparent, while the nucleus is rendered 

 distinct. 



To another drop of blood add distilled water. The cor- 

 puscles become swollen up and partly dissolved, and the 

 colouring matter (hemoglobin) 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 serum. 



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 epiderm 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 Ran- 

 vier'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 wrth the high power.) 



Note the minute, more or less conical cells of columnar 

 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 speci- 

 mens previously treated with alcohol, add a trace of acetic 

 acid, wash with water (salt solution need only be employed 

 in the case of fresh tissues), and add glycerine. Sketch. 



3. Ciliated Epithelium. Snip off a very small bit of 

 mucous membrane from the roof of 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 rela- 

 tively 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. 



Perform experiment described on p. no to show the 

 action of the cilia as a whole in the entire animal. 



