XXXVI] CELL-DIVISION 289 



Numerous dividing nuclei but with small nuclear fibres will 

 be seen in transverse sections of a limb of a young chick (2 to 

 3 cm. in length) or in any young foetal mammal. 



Hardening. The tissue should be placed in the hardening 

 agent in as fresh a condition as possible. 



Flemming's fluid and Hermann's fluid preserve the figures 

 with least alteration and allow a sharply defined stain. 

 Hermann's fluid is said to be better for the spindle fibres. 



The staining is as good, if not better, after hardening in 

 mercuric chloride, chromic acid '2 p.c., or saturated aqueous 

 picric acid, but the nuclear figures are less perfectly preserved. 

 Glacial acetic acid up to *1 p.c. may be added to the chromic 

 acid in order to make the spindle fibres more distinct. 



Potassium bichromate and other solutions of chromic salts do 

 not give good results. 



Staining. After staining in saffranin (cp. p. 286), sections 

 may be stained with gentian violet, thus 



The sections are placed for a few minutes in a gentian violet 

 solution, prepared as follows : 



4c.c. of aniline oil are added to lOOc.c. water, well shaken and 

 filtered ; to the filtrate are added 5 c.c. of a saturated solution of 

 gentian violet in absolute alcohol. 



The sections are rinsed in water, placed in iodine and iodide 

 of potassium till they are black, then decolourized to the proper 

 extent with alcohol (Hermann). 



Weigerfs hcematoxylin solution. Dissolve* 1 gram of hsema- 

 toxylin in 10 c.c. of absolute alcohol, and add 90 c.c. of water. 

 Leave for a month before use ; when used, filter and add to the 

 stock. If it is necessary to use a fresh solution, add iron-alum 

 to it drop by drop till it has a dark tint. 



In many cases '5 p.c. aqueous hsematoxylin gives a stain 

 which is not appreciably different from that given by Weigert's 

 heematoxylin. 



Larva of Chironomus. If the head be torn off, the salivary 

 glands remain attached to it as two small transparent masses ; 

 these can be examined fresh in the blood of the larva ; and then 



L. 19 



