258 SUMMARY OF CURRENT RESEARCHES RELATING TO 



that he eventually found in aceton a medium for fixing the larvae 

 without dissection, as in the foregoing procedure. After an immersion 

 of 2 to 3 hours, the larvae were transferred to 50 p.c. alcohol. 



Preparing Disease-carrying Insects.* — A. E. Hamerton first strips 

 off some pieces of the chitinous wall of the head, thorax, and abdomen 

 and at once immerses the insect in the fixative, or dissects out the parts 

 to be examined in the fixative. After an immersion of from 1 to 6 

 hours the material is transferred to 60 p.c. alcohol. A good fixative is 

 picro-acetic acid (saturated solution of picric acid 100. acetic acid 1), 

 which must be washed out with alcohol ; it is more rapidly extracted 

 with warm alcohol to which a little lithium carbonate has been added. 



Other useful fixatives are : — 1. Saturated solution of sublimate, with 

 2 p.c. glacial-acetic acid. 2. Absolute alcohol 1, glacial-acetic acid 1, 

 chloroform 1 ; sublimate to saturation ; time, a few seconds to a few 

 minutes. As soon as the objects become opaque, they are transferred to 

 70 p.c. alcohol. 3. Flemming's solution ; time, one to many hours or 

 days ; the fixative must be thoroughly washed out in running water. 



The next step is to dehydrate in upgraded alcohol, from 10 to 100 p.c. 

 The object is then imbedded ; into a test-tube is poured sufficient cedar- 

 wood oil to cover the object, and on the top of the oil a thin layer of 

 absolute alcohol. The dehydrated tissue is then placed on the layer of 

 alcohol, and when it has sunk to the bottom of the tube it is left for 

 ^ hour or so in paraffin of low-melting point, say 50° C. A second 

 paraffin bath is advisable ; time of saturating, 1 to 3 hours. When 

 quite soaked with paraffin, a block is made as follows. Place a thin layer 

 of glycerin in a Petri dish and heat slightly over a spirit lamp ; then 

 pour over the glycerin a thin layer of the melted paraffin : and when 

 this is beginning to solidify, pour in the rest of the paraffin, together 

 with the pieces of tissue, and arrange them with a hot needle. Immerse 

 the Petri dish in cold water, and then the paraffin cake will float off. 

 Blocks are then cut out and trimmed for the microtome. 



When dealing with chitinous structures, the material, after washing 

 out the fixative, should be boiled gently for about 1 hour in 10 p.c. KHO. 



For studying the mouth-parts of biting insects, the following pro- 

 cedure for keeping the component parts in their natural position is 

 given. Take four small test-tubes. In tube i. make a saturated solution 

 of gum-acacia in ether. In tube ii. make a thick syrupy solution of 

 celloidin in ether. Mix the contents of these two tubes in equal 

 quantities in tube iii. When proceeding to cut sections, take another 

 tube, iv., and put into it 2 c.cm. of ether and a few drops of absolute 

 alcohol. Then with a camel-hair brush moistened in water take a drop 

 or two from tube iii. and mix it well with contents of tube iv. With 

 this mixture paint the surface of the paraffin block after cutting each 

 section. When fixed to the slide these sections must be treated with 

 ether to remove the celloidin. 



The sections are stuck on the slides by Mayer's albumen method, 

 stained with Grenacher's alcoholic-borax-carmin, Delafield's hasrna- 

 toxylin, or Heidenhain's iron-alurn-hagmatoxylin, and mounted in balsam. 



* Journ. Roy. Army Med. Corps., xi. (1908) pp. 243-9. 



