ANIMAL NUTRITION DISCUSSION AT DUNDEE 431 



one animal was 12T per cent, of the live-weight increase. Calcu- 

 lating from the results of previous experiments extending over 

 the years 1905-8 and choosing only those lots which were 

 fed on the same or similar diets, numbering 102 pigs having an 

 average initial live weight of 97 lb., the probable error for one 

 pig works out to 137 per cent, of the live-weight increase. 

 Both sets of figures give practically normal frequency curves. 

 The differences mean that twenty-one or twenty-seven pigs 

 are necessary to determine with any degree of certainty a 

 difference of 10 per cent, between different foods and that thirty 

 or thirty-eight pigs are required to determine a difference of 

 10 per cent, in either direction. These differences, though not 

 large, point to the advisability, when calculating the probable 

 error, of taking into account age and weight of animal at com- 

 mencement of the experiment and of considering whether the 

 data are drawn from one complete experiment or from several 

 experiments extending over a number of years. 



Fifty female pigs in the latter experiment gave a probable 

 error of 13-5 per cent, of the live-weight increase and fifty male 

 pigs 13-8 per cent. 



Wood gives about 14 per cent, of the live-weight increase 

 on the probable error for cattle and sheep. His method of 

 calculation is followed here. 



In connexion with the variation and sampling of oat straw, 

 using data from a hundred individual straw analyses, the pro- 

 bable error was very great and varied according to whether 

 it was calculated on the percentage of nitrogen, the total weight 

 of nitrogen or the dry matter of individual straws, respectively. 

 Except in the case of the total weight of nitrogen the frequency 

 curves were abnormal. Similar variations were found in the 

 probable error and frequency curves calculated on the different 

 constituents of the mangel. 



A NOTE OF CAUTION 

 (Dr. Crowther) 



From no part of his work has the agricultural chemist in 

 the past derived less real satisfaction than from his efforts to 

 harmonise farm practice in feeding animals with the views 

 dominant from time to time amongst physiologists as funda- 

 mental principles of animal nutrition. 

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