26o PREPARATION OF SECTIONS 



acid are hard on the eyes, nose, mouth, and lungs, and the 

 face should be kept away from them. 



About twenty times as much Flemming's fixative should be 

 used as of material to be fixed, and the material should be cut 

 into pieces not greater than 2 rr.m. in any dimension, so that 

 the fixative may penetrate quickly to all parts. It is conveni- 

 ent to do the fixing in small phials, and if the material has a 

 tendency to float it may be pushed under with a piece of filter 

 paper that tightly fits the phial. Material should be fixed at 

 once after it is gathered and if it grows at any distance from the 

 laboratory the fixative should be taken along. 



Keep the material in the fixative for forty-eight hours and 

 then remove it and pin it in little cheese-cloth bags which one 

 can quickly make himself of the size wanted, and put these in 

 running water for about six hours, or over-night. If running 

 water cannot be had then place the material in a bucket of 

 water which is to be changed several times. 



A simpler and cheaper fixative which gives good results, but 

 not quite equal to the above for dividing nuclei, is the chrom- 

 acetic fixative. This is made by dissolving i gram of chromic 

 acid in 99 c.c. of distilled water and adding 0.5 gram of glacial 

 acetic acid. Use as described for the above fixative. 



The Hardening Process. — The material still kept in the 

 bags is, after washing, placed in 20 per cent, alcohol for two 

 hours, and then it is carried through a series of alcohols, each 

 of the series 10 per cent, stronger than the one before it, remain- 

 ing in each grade of alcohol for two hours until absolute alcohol 

 is reached. If the material is not to be imbedded in paraffin 

 at once it may be left in the 70 per cent, alcohol until needed, 

 and then it may be carried on into the higher grades as if no 

 interruption had occurred. 



The process of hardening may be considered complete when 

 the 90 per cent, grade of alcohol has been reached, and the 

 sojourn in absolute alcohol is intended to complete the dehy- 

 dration of the material preparatory to its imbedding in paraffin 

 or celloidin. In order to make dehydration more certain it is. 



