706 SUMMARY OF CUERENT RESEARCHES RELATING TO 



brush with a mixture of equal parts of alcohol and aqua ammoniEe, and a 

 slight rubbing will clean the slide with very little danger. 



After removing the superfluous balsam and cleaning the slide, finish 

 by spinning a ring around the cover with a transparent cement. 



Preparing Central Nervous System of Lumbricus.* — If the earth- 

 worm is to be sectioned in toto, it is necessary to remove the sand from 

 the alimentary canal. For this purpose, place the worm in a glass 

 cylinder partly filled with fine bits of wet filter-paper. As the paper is 

 swallowed the sand is expelled, and at the end of about two days the 

 alimentary tract is cleansed. 



In the study of the ventral cord, Dr. B. Friedlander employed the 

 following methods : — 



Place the worm in water, to which a little chloroform has been 

 added, and it soon becomes stupefied in an outstretched condition. 

 Then cut open the body-wall along the median dorsal line, and pin the 

 edges down in a dish covered with paraffin or wax. After removing 

 the alimentary canal, the specimen may be treated with a preservative 

 fluid. 



1. Osmic acid 1 per cent. After an exposure of about half an hour, 

 the worm is sufficiently stiffened to allow the pins to be removed, and it 

 may then be cut into pieces of any desired length. The pieces are then 

 left twenty-four hours in the same solution, then washed and passed 

 through the usual grades of alcohol. Preparatory to imbedding in 

 paraffin the pieces are saturated with chloroform or toluol. This 

 method is excellent for the study of the neuroglia-like elements, and is 

 the best for the brain. 



2. Preparations treated thirty minutes with osmic acid (1 per cent.) 

 are transferred to a dilute solution of pyroligneous acid (one part to 

 three parts water), which reduces the osmic acid very quickly. This 

 is followed by alcohol as before. The ganglion cells are well 

 preserved. 



3. The preparation is first treated with weak alcohol, then with 

 stronger grades. After half an hour in 70 per cent, alcohol, it is stiff 

 enough for removing the pins and for cutting into small pieces, Nerve- 

 fibres are somewhat contracted by this method, and are thus more easily 

 distinguished from the surrounding connective tissue. 



4. Corrosive sublimate (aqueous sol.) and 50 per cent, alcohol in 

 equal parts (thirty minutes) gave good preparations of the nerves and 

 the neural tubes. 



For preparations according to No. 3, the best stain is a modified 

 form of Mayer's alcohol-carmine, absolute alcohol beiug substituted for 

 80 per cent. Sublimate preparations are successfully stained with 

 Grenadier's hsematoxylin. After half an hour in this staining-fluid, the 

 preparations are transferred to acidulated alcohol (50 per cent., with a 

 little hydrochloric acid) half a minute, then placed in alcohol containing 

 a few drops of ammonia. Connective tissue and nerves are unstained, 

 while ganglion cells are stained deep blue. 



The last two methods of staining may be followed by picric acid, 

 which stains the uncoloured elements yellow. The process is as follows : 



After the sections have been fixed to the slide with collodion and the 



* Zeitschr. f. Wiss. Zool., xlvii. (1888) p. 48. 



