798 PATHOGENIC PROTOZOA 



in the third jar put diluted Hanson's stain, about 0.5 c.c. to 50 c.c. 

 water, and in this the smear remains one-half minute; in the fourth 

 bottle or tumbler put distilled water, in which the slide is washed 

 quickly and then dried. This method, for the average man, is more 

 economical and simpler than the open method. Stained smears are 

 examined directly in immersion oil without the use of cover glass. 



Hanson's stain is prepared as follows: 



Two grams of methylene blue, medicinally pure (Hochst), is 

 added to 100 c.c. of a boiling 5 per cent solution of borax. This stain, 

 though not permanent, will last a long time. It is used chiefly for 

 the diagnosis of malaria. It is diluted before use. Stain for ten to 

 fifteen seconds. 



When parasites are few, as in latent malaria, thick films may be 

 used, as first proposed by Ross. A large drop of blood is spread 

 thickly on the side, with the needle or pen used in puncturing the 

 ear ; after drying, it is put into (1) 95 per cent methyl alcohol to which 

 1 per cent of hydrochloric acid has been added, until the smear has 

 been hemolized; (2) it is then thoroughly washed in running water, 

 (3) and then stained in the usual way with a methyl alcohol stain. 

 Although the method takes considerable practice, it is a valuable pro- 

 cedure. 



