V 

 METHODS OF FIXATION 



The worker who plans extensive study on fixed eggs will 

 consult any one of the many books on microscopy and on microt- 

 omy for the methods of fixation and staining. There are in 

 addition various journals for technique in microscopy. Finally, 

 almost every text-book of histology devotes some pages to 

 methods for preparing tissues for microscopic study. Thus, 

 there is no good reason for my giving an exhaustive treatment 

 of the subject. As in the foregoing pages, I here confine myself 

 to some methods that have proved valuable to me in the course 

 of thirty years of experience with animal eggs. 



The Value of Fixed Eggs 



Undoubtedly there are shortcomings to the use of fixed cells. 

 Certainly, the experimental embryologist, as any investigator 

 interested in protoplasmic behavior in its living and completely 

 viable condition, needs to be careful In drawing conclusions 

 concerning processes in the living organism on the basis of too 

 great, to say nothing of exclusive, emphasis on the fixed object. 

 The fixed cell, as a dead cell, can obviously give us only a pic- 

 ture of what was once alive. On the other hand, the permanence 

 of structure in the fixed cell argues very strongly that the com- 

 ponents have place in the living. Thus the cellular structures 

 which have been most carefully worked out are those which 

 withstand to the greatest degree changes brought about through 

 fixation, as, for example, the nucleus and its components, the 

 chromosomes. These, the most rigidly static structures in the 

 cell, suffer least in fixation. The study of fixed cells does not 

 deserve the wholesale objection often raised against it. If the 

 experimental embryologist appreciates the limitations of fixation, 

 he can use it to great advantage. The study of the fixed egg is 

 a valuable aid, supplementing observation and experiment on 



the living. 



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