14 MICEOSCOPY. 



the fine-adjustment. When using- the microscope it is always a good 

 plan to keep the hand upon the fine-adjustment, using- it constantly 

 to bring- different planes of the object into the field of vision. 



To determine the magnifying power. Place upon the stage a stage-mi- 

 crometer and focus with both eyes open. The lines upon the microm- 

 eter will also be seen by the eye not in use. Place under the microscope 

 or upon the stage a sheet of white paper. Now, with a pencil mark 

 the apparent, or magnified, distance between two lines. Knowing the 

 real distance, one-tenth of a millimeter, the magnification can readily 

 be determined. For example, should the magnified distance between 

 two lines be thirty millimeters, the real distance being one-tenth of 

 a millimeter, the magnification would therefore be ten times thirty, 

 or 300. 



Microtome. The microtome is an apparatus employed in cutting 

 microscopic sections of tissues. It is provided with a microtome 

 knife, a knife-carrier, and the milled-head which operates a mechan- 

 ism for regulating the thickness of the sections. The student micro- 

 tome manufactured hy the Bausch & Lomb Optical Company, of 

 Eochester, N. Y., is a most excellent instrument for all ordinary 

 work. 



Paraffin Bath. This is designed for use in infiltrating and em- 

 bedding tissues in paraffin. The heat should be so regulated as 

 to keep the paraffin as near the melting point as possible. Where 

 gas is available this may be accomplished by means of a thermostat. 



Cornet Forceps. This is a forceps especially useful in holding 

 cover-glasses when staining preparations of sputum, bacteria, etc. 



Centrifuge. This apparatus utilizes the centrifugal tendency 

 and is employed to separate substances of different specific gravity. 

 It is provided with two important attachments, the sedimentation 

 tubes and carrier and the haematokrit. The sedimentation tube 

 contains fifteen cubic centimeters and is graduated into 100 equal 

 parts, up to ten cubic centimeters, and above that each cubic centi- 

 meter is graduated into four equal parts for the measurement of re- 

 agents employed. Tty means of these the solid matter in urine, 

 water, etc. may be precipitated and the exact per cent determined. 



The haematokrit is provided with graduated tubes; each tube is 

 fifty millimeters in length and is divided into 100 equal parts. The 

 diameter of the bore is 0.5 millimeter. These tubes are used in deter- 

 mining the percentage composition of the blood. By revolving the 

 handle of the centrifuge seventy-seven times in a minute the haema- 



