368 SOME ZOOLOGICAL METHODS. 



of 100 parts of 70 per cent, alcohol with 3 parts of iodine ; and 

 after fixation washes out with 70 per cent, alcohol until all 

 the colouration due to the iodine has disappeared. 



I can recommend as a good fixing and hardening mixture 

 for Annelids in general, the following fluid due to EHLERS 

 (i do not know whether it has been published) : To 100 c.c. 

 of chromic acid of 0*5 to 1 per cent, add from 1 to 5 drops of 

 glacial acetic acid. The proportion of acetic acid indi- 

 cated is sufficient to counteract any tendency to shrinkage due 

 to the chromic acid. 



735. Blood-vessels of Annelids (KUKENTHAL, Zeit. f. wiss. Mik., 

 1886, p. 61). The animals should be laid open and put for 

 two or three hours into aqua regia (4 parts of nitric acid to 

 two of hydrochloric acid). The ramifications of the vessels 

 will then be found to be stained black, the rest of the prepa- 

 ration yellow. 



736. Hirudinea. WHITMAN (Meth. in Mic. Anat., p. 27) 

 recommends that they be killed with sublimate. This reagent 

 kills leeches with such rapidity that they die in general with- 

 out having time to change the attitude in which they were 

 found at the moment when the liquid came into contact with 

 them. 



Injection. WHITMAN (Amer. Natural., 1886, p. 318) states 

 that very perfect natural injections may often be obtained 

 from leeches that have been hardened in weak chromic acid 

 or other chromic liquid. He considers that these injections 

 are the best for the purpose of the study of the circulatory 

 system by means of sections. 



Of course Hirudinea (or any other Annelids) on which it is 

 desired to make artificial injections must be killed by some 

 procedure that leaves the tissues in a state that will allow 

 the injection to run freely. 



JAQDBT (Mitth. Zool. Stat. Neapel, 1885, p. 298) advises 

 that leeches be put into water with a very small quantity of 

 chloroform ; they soon fall to the bottom of the vessel and 

 remain motionless. They should be allowed to remain a day 

 or two in the water before injecting them. 



