Culture Techniques 143 



under consideration here, Bobbins and his col- 

 leagues have chosen a much longer period, usually 

 from a month to two months. This has certain 

 definite advantages as well as disadvantages. 

 Robbins uses dry-weight as a measure of growth. 

 By this method cultures are examined only at the 

 end of the passage, when they must be sacrificed 

 (see later). A two-month period thus requires 

 only an eighth as much work as do eight one-week 

 periods. The long period permits tissues to ma- 

 ture and might, in theory, give time for morpho- 

 logical changes to become evident that would 

 never appear in cultures maintained for repeated 

 short periods. (Compare Parker, 1936, 428, 429; 

 Fischer u. Parker, 1929, 411.) It permits the 

 accumulation of large masses of tissue so that the 

 percentage differential between the final size in 

 two different nutrients may be much greater than 

 after a shorter period. These appear to be ad- 

 vantages. On the other hand, the long period 

 permits the study of far fewer cultures in a given 

 space of time, tying up both laboratory space and 

 glassware. Contrary to expectation, morphologi- 

 cal changes which might be anticipated have not 

 actually appeared. Moreover, the large masses 

 of tissue accumulated in a long period may be 

 largely inert carbohydrate — cell-wall materials, 

 starch, etc. There is some evidence that such cul- 



