APPENDIX: 



INCLUDING THE MOST USEFUL METHODS OF HISTOLOG- 



ICAL TECHNIQUE. 



WITH the exception of the fluid tissues, as blood and lymph, scrapings 

 from organs, as the spleen and the liver, or ' ' teased ' ' fragments separated 

 with needles, as connective tissue or nerve-fibres, the tissues and organs of 

 the body are so compact and opaque that very thin sections, made transpar- 

 ent by artificial means, are necessary for satisfactory microscopical examina- 

 tion. Moreover, in order to display the structural units, it is usually desir- 

 able to stain such sections with suitable dyes, so that advantage may be 

 taken of the differences in the color affinity of the various parts of the cells 

 or of the intercellular substances to secure adequate differentiation. After 

 being stained, the sections are rendered transparent and enclosed in some 

 mounting medium, after which thy may be preserved often for years with- 

 out deterioration. 



The methods devised or modified by the many engaged in histological 

 work have resulted in the great mass of technical details described in the 

 various books devoted to the subject. Notwithstanding the value of special 

 processes for particular lines of investigation, by far the greater part of his- 

 tological work is accomplished with a few well-tried standard methods. To 

 describe the most useful of these methods, as carried out in the laboratory, 

 for the assistance 'of the student who may wish to undertake the preparation 

 of material for microscopical examination, these pages are added. No at- 

 tempt is made even to mention, much less describe, many excellent methods 

 for particular purposes. The few procedures here given, however, may be 

 depended upon to yield excellent results, when properly carried out, and in 

 the great majority of cases will be found to be adequate for the demonstra- 

 tion of structural details. The student undertaking independently such work 

 for the first time is urged to persevere with the methods here given until he 

 has repeatedly carried them to the successful results of which they are ca- 

 pable. Failures, sure to beset the beginner, should be carefully analyzed and 

 be made to yield experience guarding against their repetition. 



FIXATION AND PRESERVATION OF TISSUES. 



It is evident, that, no matter how carefully subsequent manipulations 

 be conducted, unless the tissue itself be successfully preserved, the finished 

 preparation will not present a trustworthy picture of the normal structure. 

 The tissue must be secured, therefore, as fresh as possible, since in the case 

 of delicate structures, as the epithelium lining the digestive canal, the 

 post-mortem changes occurring within a few hours are sufficient to destroy 

 interesting details. Tissues from the lower animals are readily obtained from 

 the recently killed animal, while still warm and the cells yet alive; those from 

 man are less easily secured, the early autopsy and some favorable operation 

 being the usual sources for the histologist' s stock. The manifest desidera- 

 tum being to retain, as far as possible, structural details in the condition in 



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