82 



FIXATION 



distilled water, the tubules appear shrunken in paraffin sections; 

 but when this fixative is dissolved in 0-9% sodium chloride solu- 

 tion, the epithelium of the tubules sometimes swells so much that 

 the lumen is almost obliterated in the final preparation. ^^^ Some 

 impression of the eflPect of indifferent salts on the fixation of 



140 



120 



5^ 100 





o 



< 



80 



z 60 



o 

 a. 



< 



OJ 



_i 

 O 



> 



40 



20 - 



-I 



XYLENE 



FIG. 12. Graph showing how the volume of the 

 eggs of Arbacia pustulosa is affected by the addition 

 of non-fixative salts to formaldehyde solution, at 

 various stages in paraffin embedding. Each point 

 represents the mean of 10-15 measurements. 



(From the data of Hertwig.***) 



mammalian cells can be obtained by means of the system of grading 

 described on pp. 72 to 75. It will be remembered that the grad- 

 ing is done while the judge does not know what fixative was used 

 in the preparation of the slide: his judgement is therefore impartial. 

 The results with several fixatives are shown in table 7. In no case 

 was a fixative placed in a higher grade when used without an 

 indifferent salt than when used with it. The first three fixatives 

 in the table were markedly improved by the addition of an 



