106 PRACTICAL PARASITOLOGY 



picro-sulphuric acid ; picro-nitric acid ; acetic acid solution of 

 chromium. Specimens are finished in accordance with the fixing 

 mixture, and the results are more rapid if the worms are cut into 

 lengths before fixing. 



It is essential that the dehydration of Nematodes should proceed 

 by gently graduated stages. Transference to the clearing fluid and 

 to paraffin must also be done by careful gradation. In each case 

 the fluid is changed by means of intermediate stages, the prepon- 

 derance of the new reagent being gradually increased. 



Acanthocephales are prepared in a similar manner. For fixing, 

 Kaiser recommends a saturated solution of mercuric chloride warmed 

 to about 56 to 60 C. ; or a 3 per cent, solution of the same salt to 

 which 1 per cent, glacial acetic acid has been added ; or a saturated 

 solution of mercuric cyanide (very poisonous) ; or the following 

 mixture : acid, picronitr. cryst. 1*0, ac. sulf. cone. lO'O, ac. chrom. 

 cryst. 1-0, aq. dest. lOOO'O. All these reagents should be used warm 

 (45 to 50 C.). Small objects should be allowed to soak in mercuric 

 chloride solution for five minutes, larger objects ten to thirty minutes. 

 In glacial acetic acid solution of mercuric chloride, large objects take 

 up to one hour ; in mercuric cyanide, from a quarter to one hour, 

 according to size; and in the picric acid mixture, fifteen to twenty 

 minutes. When the first fixing reagent is used, specimens should 

 be washed out with a solution of camphor in 60 to 70 per cent, 

 alcohol, warmed to a temperature of about 60 C., the specimens 

 to be left in soak for two to six hours. When the second fixing 

 reagent is used, specimens are rinsed for four to eight hours in 

 running water. In the case of the third fixing reagent, they are 

 washed out in 70 per cent, alcohol. And, where the picrin mixture 

 is used, they are first rinsed for a short time in warm water, and then 

 put into 60 per cent, alcohol for three to four- days. 



Specimens are dehydrated by means of alcohol in stages of in- 

 creasing strength ; cleared by means of alcohol and benzol in carefully 

 graduated stages to pure benzol ; and embedded by carefully graduated 

 stages of benzol and paraffin to pure paraffin. 



Hamann fixes his specimens with mercuric chloride solution, or 

 alcohol to which a few drops of solution of chloride of platinum 

 has been added. He recommends the cutting of the worm into con- 

 venient lengths in order to facilitate the action of the reagent. 



(c) PRESERVATION FOR MUSEUM PURPOSES. 



A collection of Helminthes will consist in part only of microscopic 

 preparations, such as whole objects, sections, and series of sections. 

 As a general rule, it is not possible to prepare for the microscope all 

 the individuals of a species which are found at one time. It will 



