REAGENTS 35 



ty years ago, most botanists were beginning with 35 per cent alcohol; 

 in the second edition of this book (1905) we recommended 15, 35, 50, 

 70, 85, 95, and 100 per cent as a safe series, since it causes no obvious 

 plasmolysis of the cell contents. As investigations have become more 

 and more critical, especially investigations upon the structure of 

 chromatin, it has been found that even 15 per cent alcohol is too strong 

 for a beginning. It is maintained that, in addition to the damage done 

 by transferring from water to so strong an alcohol, the final dehydra- 

 tion is not so perfect as it is when the series begins with a weaker alco- 

 hol. Yamanouchi, whose work upon delicate algae has been particular- 

 ly successful, uses the following series: 2|, 5, 7| ,10, 15, 20, 30, 40, 50, 

 70, 85, 95, and 100 per cent. After such gradual early stages, there 

 seems to be no objection to the less gradual stages which follow. Of 

 course, there is no particular virtue in the fractions: it is convenient 

 to make a 10 per cent alcohol, then dilute it one-half for the 5 per cent, 

 and dilute the 5 per cent one-half for the 2| per cent. The 7| per cent 

 is made with sufficient accuracy by adding a little water to the 10 per 

 cent alcohol. 



It is not safe to suggest minimum times for each grade of alcohol. 

 One might as well recognize that in histological technique speed and 

 excellence seldom go together. For the first six grades, three grades a 

 day, morning, noon, and evening, seem to be safe: for 30, 40, 50 and 

 70, two grades, morning and evening; 85, for 24 hours, changing the 

 alcohol 2 or 3 times, since this is the best place for hardening; 95, for 

 24 hours; for the absolute alcohol, 24 hours, with 2 or 3 changes, 

 should complete the dehydration. 



If pieces are larger than |-inch cubes, the times should be longer. 



In all cases, the absolute alcohol should be changed 2 or 3 times. 

 The grades below 85 per cent can be used repeatedly. The absolute 

 alcohol should not be used again for this purpose, but may be put back 

 into the 95 per cent bottle. It is always well to filter the alcohols when 

 pouring back into the bottle. Otherwise, there would soon be an accu- 

 mulation of starch grains, pollen grains, spores, and various other 

 things. Waste alcohol as strong as 85 or 95 per cent will be useful for 

 rinsing one's hands when dealing with Venetian turpentine. If it is 

 necessary to be very economical, the stronger alcohols may be filtered 

 into a single large bottle and the strength of the mixture can then be 

 determined by using an alcoholometer. Knowing the strength of the 

 mixture, one can easily make any weaker grade. 



