32 Methods in Plant Histology 



fixed in an aqueous solution, it must pass through a series of alcohols 

 of increasing strength, beginning with about 3 per cent alcohol. Ten 

 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 dehydration is not so perfect as it is when the 

 series begins with a weaker alcohol. Yamanouchi, whose work 

 upon delicate algae has been particularly successful, uses the following 

 series: 2J, 5, 7J, 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 7J per cent is made with sufficient 

 accuracy by adding a little water to the 10 per cent alcohol. For 

 each of the first four or five grades, 3 or 4 hours is long enough. It 

 is a good plan to change morning, noon, and night. From the 20 to 

 the 95, change morning and evening. About 24 hours, changing 

 two or three times, is not too long for the absolute alcohol. The 

 grades of alcohol below 100 per cent can be used several times. The 

 absolute alcohol should not be used again for this purpose, but it 

 should be saved and used for rinsing slides after the paraffin ribbons 

 have been dissolved off with xylol or turpentine. Even 85 and 95 

 per cent alcohol 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. 



Be sure that the bottles or Stenders for absolute alcohol are 

 perfectly dry ; keep the bottles well corked and keep the lids on 



