LABORATORY AND TEACHING METHODS 



657 



The circulation of the ice-salt water is accomplished by allowing it to drip from 

 a small orifice at the end of the glass tube C. 



The block of frozen mucilage with the contained substance held on the freezing 

 plate is then cut with the hand microtome or with the design of microtome shown 

 on the next page. 



Or the material may be frozen in the design of freezing chamber shown on page 

 659 and sectioned by Spencer automatic laboratory microtome No. 880, as indicated 

 in the accompanj-ing figures. If mucilage is used it can be removed by placing the 

 sections as rapidly as cut in warm water. 



CO2 Freezing Allachmcnt. — The freezing device in this attachment consists of a 

 small metal cylinder. The object is placed on the flat disk top of the cylinder, 



Fig. 231. — Freezing attachment for use of CO2 in freezing microtome. 



which measures 36 mm. in diameter, and is frozen by the expansion of the CO2. 

 This device is connected with the gas cylinder by a flexible copper tube, provided 

 with a connecting nut for joining to the cylinder and the necessary adapter for fitting 

 to the microtome. It is furnished also with an extra valve, which can be placed at 

 either end of the tube. 



CO2 gas furnishes the most rapid and convenient medium for freezing specimens 

 and can be used in this attachment with either the table or physician's microtome 

 (Figs. 231, 232). An ether attachment is also used (Fig. 233). 



LESSON 44 



Use of Drawing and Projection Apparatus. — The author has found it an excellent 

 training for students to learn the use of the drawing apparatus designed by Edinger, 

 as well as the new Spencer photomicrographic camera. These pieces of apparatus 

 can be used for drawing, for projection and for photomicrography. 

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