LABORATORY METHODS IN MALARIA 379 



a longer fixation will do no harm. When the preparations are 

 fastened to slides it is usually more convenient to wash them in 

 water before transferring them to the alcohols for subsequent 

 washing and dehydration. 



Staining. Mayer's acid hemalum is an excellent stain for stom- 

 achs and salivary glands. It is precise and usually does not over- 

 stain. It may be used undiluted or diluted in distilled water. Borax 

 carmine is also recommended for this sort of material. 



In mosquito, as in other material, it is difficult to lay down 

 definite rules for the length of time a specimen should be stained. 

 The character of the material itself, its fixation and the dilution 

 of the stain are important factors. It is always best to control the 

 process by examination under the microscope while the staining is 

 in progress. 



A few general rules may be of assistance : "Free" specimens 

 stain more rapidly than those fixed to a slide. Specimens stained 

 under coverglasses should be kept at least over-night in acid 

 hemalum. A light stain is preferable for the demonstration of 

 oocysts on a stomach wall since a heavy stain tends to obscure 

 them. Stomachs fastened to the slide but without a coverglass 

 may be sufficiently stained by a treatment of one hour in Mayer's 

 acid hemalum diluted one to ten in distilled water. It is always 

 necessary to treat specimens stained in hemalum with some alkaline 

 fluid to fix the stain. Most tap waters, or alcohol slightly alkalin- 

 ized by a few drops of a one per cent solution of sodium carbonate 

 will serve. Counterstaining is usually unnecessary. If it is desired, 

 preparations may be counterstained in one of the higher alcohols 

 to which eosin or some alcohol-soluble dye has been added. 



Dehydration and clearing of mosquito stomachs require a little 

 more time than do sections. Material may be left a long time in 

 the higher grades of alcohol. It is best to avoid passing from one 

 medium to another of a much higher or lower concentration, 

 especially in dealing with large hollow organs liable to collapse. 

 In general, however, a specimen is not harmed by more abrupt 

 transfers, provided it is well fixed and hardened. It is assumed 

 here that the demonstration of finer cytological details is not re- 

 quired. I Ij^I; 



Labels may be written on the slide with a diamond pencil, pref- 

 erably at the time of fixation. If desired, paper labels may be sub- 

 stituted after the preparations are stained and mounted in balsam. 



