//. Criteria of Successful Processing 



W'c ha\c carried to completion the processing of some plant ma- 

 terials and have the finished slides before us. Our notebook contains 

 a record of the entire process, from collecting the living plants to 

 the completion of staining. We can now examine the slides critically 

 and consider the criteria by which we may judge the success or 

 failure of the processing. The severity of our scrutiny depends on the 

 objectives of the stud) for which the preparations were made. We 

 may be primarily interested in the distribution of tissue systems or 

 the position of organs, j^aying little attention to the protoplasm. 

 Rapid and convenient methods that preserve the desired structures 

 with adequate accuracy need not be regarded as slovenly. Another 

 study may require the preservation of the constituents of the proto- 

 plasm in their normal structure and position. The use of more 

 elaborate, time-consuming jjrocesses is then justified. 



It is axiomatic that slides for elementary students must be nuich 

 more perfect than for advanced workers. Beginners waste much time 

 puzzling over imperfections. They will draw faithfully a break pro- 

 duced in microtoming, the gap between the cell wall and the col- 

 lapsed plasma membrane, or a sjjeck of debris in the tissues. 



Tlie j)athologist should be especially critical. Control slides of 

 noinial tissues nuist show cellular details with almost diagrammatic 

 perfection in order to furnish a basis for interpreting pathological 

 conditions. Studies in physiology, (violog). and experimental mor- 

 phology also demand careful control of processing and critical exam- 

 ination of slides on the basis of some useful criteria. 



The following ilhisi rat ions Avere selected Irom well-known and 

 widely used subjects. Leaves of different species exhibit different re- 

 actions to killing fluids. The quality of the fixation can be determined 

 easily by the condition of the j^alisade cells. The outlines of the cells 

 should not be wrinkled, and the chloro})lasts should line the walls. 

 Figure ll.l a shows the excellent preservation of cellular and tissue 

 detaiK in soybean leaf, a highly spongy and therefore dilficult subject, 

 processed as oiulined in the legend. 



[ 110] 



