CHAPTER XXIV 

 TECHNIC 



THE technic of cytological and histological research has assumed 

 formidable and intricate proportions of detail. Its fundamental ideas, 

 however, remain the same and probably 95 per cent of the de- 

 tailed modern methods are based upon, or elaborated from, these first 

 principles. 



The student is advised to read and digest the following general outline 

 of the principles of technic, and then execute the several complete sched- 

 ules. After this, if he wishes to further master technic, he should pre- 

 pare for study the specimens which appear in each chapter, following 

 the outline directions given in special cases, and these will afford him 

 a sufficiently varied and extensive practice for all purposes. The "Micro- 

 scopist's Vade Mecum," by Lee, should be at hand and referred to in 

 this connection. 



The methods are in all cases the best that the writers have actually 

 had experience with. They are not picked out with reference to an 

 inexperienced student and a poorly equipped laboratory, but call for the 

 best of instruments and reagents, and an experienced instructor. In 

 different hands, other methods will sometimes be found to do the work 

 better in certain cases, and the examples found below are offered as a 

 convenience or a starting-point. 



GENERAL OUTLINE 



Most tissues cannot be studied in a fresh condition because of several 

 obstacles ; they are too thick and cannot be cut into thin slices on account 

 of their texture. Besides, their parts are nearly of one common color 

 and refractive index, which makes the structure indistinct at the best, 

 and, lastly, they will soon decay or dry and are not permanent. 



So our technic is devised to get slices thin enough to see, to change 

 the color and refractive index to more favorable conditions, and to make 

 more or less permanent preparations. 



The majority of tissues containing much protoplasm must first be 

 fixed, which means killed by some medium that leaves them in a con- 



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