MICROLITER DIVER TECHNIQUE 



345 



illuminated in a manner which will nut heat the bath. This requires 

 that the back of the thermostat also be made of glass. Local heat- 

 ing must be avoided at all costs. Hence, if it is necessary to have 

 strong illumination on the divers, as is the case when observations 

 are to be made of organisms placed in the diver for study, a special 

 arrangement for submerging the light source in the thermostat will 

 probably have to be made. For this purpose Holter employed lamps 

 placed in a trough made of ground-glass plates cemented together. 

 The trough was lowered into the thermostat and filled with water to 

 the water level of the thermostat. The water in the trough was 

 cooled by a cooling coil to keep the temperature a few tenths of one 

 degree below that of the thermostat. 



Fig. 112. Arrangement of Cartesian 

 diver apparatus. 



<S, Syringe to vary pressure 



Mu, mercury manometer 



AIw, water manometer 



B, air bottle 

 From Rocher (1943) 



Convection currents in the flotation vessel, which may result from 

 local heating, can be detected by pipetting a colored solution of the 

 same density as that of the medium into the flotation vessel to form 

 a colored layer in the bottom third. Any convection movement will 

 produce colored streaks in the medium. 



(2) FLOTATION VESSELS 



A flotation vessel and its clamp are illustrated in Figure 113. A 

 standard-taper ground-glass joint is used to connect the vessel 

 through rubber pressure tubing to the manifold which leads to the 

 manometer. All parts not surrounded by thermostat water, here as 

 elsewhere in the apparatus, must be made small and thick-walled to 

 reduce the air space. The angle of the conical bottom of the vessel 

 should not be too small, since it is well to reduce the surface of 

 contact between the end of the diver tail and the bottom of the 

 vessel to a minimum. Otherwise there is a tendency for the tail to 

 stick to the bottom. 



