METHODS OF RESEARCH: TECHNIC OF ISOLATION 109 



any vegetable fragments be left there to mold later on. Select 

 for isolation experiments the most recently diseased parts of 

 the freshest material available. Further, because saprophytes 

 often supplant parasites very speedily in diseased tissues and 

 because even in the absence of these there may have been whole- 

 sale death of the parasite owing to the acids or other by-prod- 

 ucts it has liberated, thick sowings and other special devices 

 are often necessary in order to isolate the cause of the disease. 



CARE OF CULTURES 



Room Temperatures. — When first made, the plates naturally 

 must remain for a short time on a level shelf in the culture room, 

 but as soon as solidified they must be removed to a suitable 

 safe place for incubation, viz., to a clean dry cupboard, free 

 from insects and protected from the hght, at least from direct 

 sunlight, or bright reflected light. If the laboratory is a 

 clean one there should be little trouble from the larger vermin 

 such as rats, mice, flies or cockroaches, but minute animals such 

 as mites and small ants often live in the walls of buildings, be- 

 yond reach, and may sometimes cause much annoyance in clean 

 places. We have been troubled with both of these pests and 

 now, as a routine practice, keep our plates and other cultures on 

 shelves supported on cork legs resting in glass dishes containing 

 mercuric chlorid dissolved in water, but after the water has 

 evaporated more need not be added since the crystals uniformly 

 distributed over the bottom of the plate are a sufficient barrier. 

 The shelf, of course, should not anywhere touch the walls of the 

 cupboard. This has proved quite effective. The pest of ants 

 may be done away with by finding and destroying the nest, 

 which is sometimes a long distance away. A good plan is to 

 drive deep holes into the ground by means of a crow bar and 

 fill these with kerosene. Record the temperature daily. 



Thermostats. — These are usually only for temporary use and 

 the temperatures are to be shifted as needed, or rather some days 

 in advance of the need, since often they are hard to regulate. 

 We use the Roux metal-bar thermo-regulators. 



