260 THE PROTOZOA 



2. Fix five to thirty minutes in a mixture of equal parts of absolute 

 alcohol and ether. 



3. Dry between two pieces of filter paper. 



4. Stain in a watery 'solution of methylene blue ; wash with water. 



5. Contrast stain in a 2 per cent, solution of eosin in 60 per cent, 

 alcohol. 



PLEHN'S METHOD. 



Stain. 



Methylene blue concentrated watery solution, . . 60 

 J per cent, eosin solution in 75 per cent, alcohol, . 20 

 Aqua distillata, ........ 40 



1. Place the specimen in the stain five to ten minutes. 



2. Wash in water and dry. 



3. Mount in xylol balsam. 



Results.- The cells containing haemoglobin are stained red, the plasma 

 and body of the parasite a more or less intense blue. 



Many other staining and fixing methods are used, but examination of 

 the fresh specimens and staining by the above-mentioned methods will 

 be found sufficient for diagnostic purposes. To observe the nucleus 

 substance, the ordinary methylene blue method is sometimes sufficient, or 

 the specimen is fixed in a mixture of acetic and picric acids and stained 

 with haemotoxylin, or examined in fresh blood to which some methylene 

 blue or fuchsin is added. 



Mode of Infection. The cultivation of the parasite of malaria has 

 not yet been accomplished, and infection of animals has also not 

 succeeded. The parasite is only known as a parasite of the blood of 

 man, and of where and in what manner they exist outside the body 

 nothing is known, therefore the knowledge of the mode of infection is 

 very limited. Malaria can be communicated from man to man by means 

 of the blood. Gerhardt did it subcutaneously, and later it was accom- 

 plished both by subcutaneous and intravenous injections of the blood of 

 malarial patients. Nevertheless, malaria is not a contagious disease ; it is 

 not communicable from man to man under natural conditions. The 

 parasite is not found in the secretions, but it appears to be present in 

 the herpetic vesicles of malarial patients, because the contents of the 

 vesicles are capable of transmitting the disease by inoculation. The 

 parasite undoubtedly exists in certain swampy districts, endemic, and at 

 certain times epidemic, in a saprophytic condition in either the earth, 

 water, or air. The transmission by means of the bite of insects is 

 theoretically possible, and by some authorities it is advanced, but it has 

 not yet been satisfactorily demonstrated. The incubative period in the 

 majority of cases is from eight to fourteen days ; but cases are known 



