CHAPTER XXXVL 527 



applicable, but numerous modifications have been introduced to 

 meet special cases. Speaking generally, the main lines of study 

 applied to the protozoa may be summed up under the following 

 headings : Culture, collection, determination of life cycles, general 

 morphology, physiology. It will perhaps be appropriate to say a 

 few words by way of introduction under each of these headings. 



995. Culture. No general method is applicable to all cases ; for 

 many of the free living protozoa, such as infusoria, amoebae and 

 flagellates, a simple 1 or 2 per cent, hay infusion is suitable, which 

 may be conveniently placed in small petri dishes ; these give the 

 additional advantage of providing a large surface. Amoebee are in 

 many cases best grown on a solid agar medium, to be described later. 

 Special media have been described for the culture of many patho- 

 genic forms, such as trypanosomes, and quite lately Sr. Monica 

 Taylor has described a useful method for cultivating Amoebae 

 proteus ( 1013). 



996. Pure Mixed Cultures of Amoebae. When working with 

 protozoa it is extremely desirable to have pure cultures whenever 

 possible. In the case of amoebae, bacteria are necessary as food, so 

 that we must grow our amoebae with bacteria. A culture containing 

 one species of amoeba, together with a pure culture of any particular 

 bacterium, is spoken of as a pure mixed culture, and it is necessary 

 to obtain such pure mixed cultures in order properly to study the 

 biology of the amoebae. The preparation of a pure mixed culture 

 involves two distinct processes : (1) The separation from its fellows 

 of a single amoeba ; and (2) its subsequent cultivation with a pure 

 culture of some selected bacterium. 



(1) Separation of a Single Cyst. The easiest method of accom- 

 plishing this is by means of the following method. Take a glass 

 capillary tube about 5 to 10 cm. in length and 1 mm. in diameter. 

 Flame the centre, and draw out quickly to the fineness of a hair. 

 Break into two equal portions and reduce each of these to a length 

 of 5 cm., so that one obtains two short tubes consisting of a wider 

 portion and a very fine capillary portion. Next select a culture of 

 the amoebee rich in cysts, add a drop of sterile water, and rub a 

 portion of the growth into this with a sterile platinum wire. Allow 

 a minute portion of this emulsion to run into the capillary end of 

 the prepared tube, and then run in sterile water till about -5 cm. 

 of the broad portion of the tube is filled. Mix the contents of the 

 tube by vigorous rotation. Now prepare an agar film on a micro- 

 scope slide, by melting one of the stock tubes of the agar and pouring 



