50 J. MYERS 



Stated water flows through the outer jacket. The algal suspen- 

 sion is contained in the inner annulus which is only about 5 mm. 

 thick. Aeration is provided through a cotton filter and in the 

 very thin annular chamber it also produces good agitation of the 

 suspension. Samples of the suspension are harvested as needed; 

 the suspension is never completely harvested, however, some 

 always being left as an inoculum. Automatic dilution is accom- 

 plished by a photometric device. As the culture grows, the in- 

 creased number of cells cuts down the illumination on a photo- 

 cell. An oiT-balance current is developed in the photocell circuit, 

 causing a relay to open a solenoid valve and allow fresh media to 

 flow in, diluting the culture back to a photometric balance. The 

 result is that the culture is maintained at a point or within a very 

 short segment of the growth curve. 



The continuous culture apparatus provides the very great ad- 

 vantage that the effects of environmental conditions may be 

 examined by introducing only a single variable at a time. Rate 

 of growth is readily determined by leaving a known amount of 

 inoculum at the end of each harvesting period and determining 

 the amount of the harvest. In addition a daily harvest of from 25 

 mg. to 250 mg. of dry weight per day provides adequate quanti- 

 ties for most types of physiological work. The method has the 

 disadvantage of requiring a considerable overhead of man-hours 

 for maintenance. It has presented so many advantages, however, 

 that we customarily maintain three units in operation. 



A second general objective in culture has been the production 

 of cellular material for metabolic studies or for chemical analysis. 

 Experimental design here depends primarily upon the quantities 

 of material needed. The most common procedure has been to use 

 flasks such as those of Figure i. By a regimen of harvesting a cul- 

 ture always at some one point on its growth curve, fairly repro- 

 ducible material can be obtained. Our procedure, wherever possi- 

 ble, is to use the continuous culture apparatus which produces 

 highly uniform experimental material day after day. 



When very large amounts of algae are needed, as for chemical 

 analysis, the quantity requirements become the deciding factor 

 in design. For investigation of photosynthesis by use of radio- 



