370 



EXPERIMENT STATION EECORD. 



investigation are very similar. However, increasing tlie size of tlie lots is no 

 remedy for a poor selection of experimental animals, nor can increased size of 

 lots eliminate tlie element of Individuality. Tlie beneficial effect of increasing 

 the size of lots varies not with the number in the lot, but with the square root 

 of this number. Uniformity of gains within the lot is desirable and can be 

 obtained by a reduction in the coefiicient of variation of gains. The experi- 

 mental error may be reduced by the selection of experimental animals homo- 

 geneous as regards age, breed, type, sex, and previous treatment. In this con- 

 nection it has been found that as a rule lots exhibiting the best average gains 

 also exhibit the more uniform gains, and vice versa ; also that the changes in 

 the variability of gains during an experiment may be materially reduced when 

 conditions are constantly or increasingly favorable to growth and fattening. 



Experimental evidence indicates that physiological selection of experimental 

 animals does not eliminate the poor gainers, and that such selection is very 

 inefficient in reducing experimental error, even when conducted along the most 

 rigorous lines. 



The difficulty which some stations have had in duplicating experiments and 

 results leads to the conclusion that the frequent tendency to generalize from 

 data of a very specific description should be carefully guarded against. It is 

 further recommended that experimental rations be submitted to a chemical 

 analysis, for *' the practical utility of average analyses Is limited, and in the 

 case of many of the grains and roughages is small, indeed." On the other 

 hand, the individual feeding of animals in ordinary feeding trials is deemed 

 unnecessary and entirely out of harmony with ordinary practice. 



In concluding this bulletin the authors present their views relative to the 

 publication of results and the formulating of results, showing wherein caution 

 and precision must be used when asserting that a given experiment indicates 

 a superiority of one ration over another. 



There are appended statistical data concerning the rate of growth of sheep, 

 swine, steers, and poultry ; formulas for determining the number of animals to 

 include in an experimental lot; additional data on the change in variability 

 of gains in weight as related to feed consumption; and a bibliography of 84 

 references. 



The element of uncertainty in the interpretation of feeding" experiments, 

 H. H. MiiTCHELL and H. S. Grindley (Illinois Sta. Bui. 165, ahs., pp. 2-8). — 

 This is a popular edition of the above bulletin. 



An investigation of the feeding value of flax material as determined by 

 chemical analysis, J. W. Ince (North Dakota Sta. Bui. 106, pp. 10-29).— This 

 article includes a summary of data as to the feeding value of flax straw and 

 flax plant by-products, with comments on the extensive use of these materials 

 in commercial stock feeds. The average composition of flax materials, as 

 shown by analyses of materials collected in North Dakota in 1912, is given in 

 the f ollovving table : 



Analyses of flax materials. 



