Lecture I. 7 



bright, and with this arrangement it is very indistinct and hard to 

 make out. This material, together with the nucleus, forms the 

 protoplasm of the cell. It forms an irregular lining to the cell- 

 wall. In places the lining is thick and in places again it is drawn 

 out to an infinitesimally thin pellicle. Embedded in the proto- 

 plasm are various smaller or larger specks which are often called 

 granules. In the cells before us, as is often the case in cells com- 

 posing tissues which have ceased to grow, the protoplasm occupies 

 but a small proportion of the space enclosed by the wall. The 

 greater part of the cavity of the cell is occupied by a drop of fluid 

 called the vacuole. Sometimes strands of protoplasm may be seen 

 striking across it or even it may be broken up into a number of 

 small vacuoles separated from one another by sheets or partitions 

 made of the slimy protoplasm. Often some of the granules seen 

 in the protoplasm are minute vacuoles. 



PRACTICAL WORK. 



Acquaint yourself with relations of the various parts of the microscope and 

 learn their names. 



Mount a piece of the leaf-skin of Tradescantia virginiana in a drop of 

 water. Cover with a clean cover-glass. 



Put the low power in position and set the preparation on the stage. 



Adjust the mirror so that light from the window is concentrated by the 

 condenser on the object. 



Focus the object and try how changes in the mirror, the diaphragm and 

 the level of the condenser alter the microscopic appearance of the object. 



Count the number of cells on the diameter of the field. 



Note the outlines and the nuclei of the cells. 



Adjust the middle of the fragment of skin to coincide with the centre of 

 the field. 



Raise the body of the microscope by means of the coarse adjustment. 

 Switch on the high power. 



By means of the coarse adjustment bring the front of the high power to 

 about 4-5 mm. from the cover-glass. 



Close the diaphragm to a small aperture. 



With your eye constantly looking into the eye-piece rack the body of the 

 microscope very slowly downwards. As soon as dark indistinct objects begin 

 to loom into view transfer your fingers to the fine adjustment, and by turning 

 it downwards bring the cells into focus. Now observe the distance of the 

 high power from the cover. When the focus has thus been obtained switch 

 back the low power and note if it is necessary to raise or depress the body to 

 bring it into focus. 



Again count the number of cells occupying the diameter of the field. This 

 will give an idea of the relative magnifications of the high and low powers. 

 Try the effects of various adjustments of mirror, diaphragm and condenser. 

 Focus for the near side and the far side of the nucleus and for its diameter. 



Carefully draw an optical section of a cell in the plane of its nucleus. 



Make your sketch on smooth paper with a sharp pencil. Your sketch 



