ArmL 10, 1885. 



SCIENCE 



29b" 



times in computing the composition of large 

 amounts of fodder from that of small samples. 

 In some recent digestion experiments made by 

 the writer at the Wisconsin agricultural experi- 

 ment-station, a computation was made of the 

 influence of these analytical errors, with results 

 very similar to those arrived at by Kiilin l in a 

 paper on the effect of cooking and other 

 methods of preparation, upon the digestibility 

 of wheat-bran. 



In both cases it was assumed that no mate- 

 rial loss of either fodder or excrement had 

 occurred. In view of the care taken in the 

 conduct of the experiments, this assumption 

 seems justified. It at least does not magnify 

 the probable error. It was likewise assumed 

 that the sampling was free from error. In the 

 writer's experiments, analyses of four samples 

 of the same ha}' agreed so closely as to justify 

 the assumption. In short, the computations 

 were confined to the effect of analytical errors 

 upon the results. 



With these explanations, we give below a 

 statement of the errors to which the several 

 determinations were found to be subject : — 



Probable errors. — Hay. 



Dry matter . . . 

 Organic matter . . 

 Proteine (N X 6.25) 

 Crude fibre . . . 

 Fat (ether extract) . 



Kiihn's experi- 

 ments. 



Per cent. 



±0.1 



±2.1 

 ±1.9 



±2.5 



Armsby's 

 experiments. 



Per cent. 

 ±0.08 



± 1.15 

 ±0.62 



It should, perhaps, be added, that the results 

 of a digestion experiment are usually expressed 

 in per cent of the amount fed. The above 

 results mean, that if, for example, 50 <% of the 

 proteine fed was found to have been digested, 

 the true amount in the writer's experiments 

 was probably not less than 48.85% nor more 

 than 51.15%. 



That the probable error appears smaller in 

 the writer's experiments is largely due to the 

 methods of calculation empkryed. No strict 

 rules can be followed in such a computation, 

 but a considerable field must be left for the 

 exercise of good judgment. Kiihn wished to 

 avoid making the error appear too small : the 

 writer, with a somewhat different purpose in 

 view, wished to avoid exaggerating it. It is 

 plain that in both experiments a reasonable 

 degree of accuracy was attained. 



Next let us turn to the results upon b} T -fod- 

 ders. Here, owing to the method necessarily 

 1 Landw. vermch^-stationen, xxix. 1. 



employed (see above), the errors are, so to 

 speak, concentrated in the by- fodder, as the 



following statement shows : — 



Probable errors. — By-fodders. 







Kiihn's ex- 

 periments. 1 



Armsby's 



experiments. 





Bran. 



Malt 



sprouts. 



: Cottonseed- 

 meal. 



Dry matter . . . 

 Organic matter 

 Proteine .... 

 Crude fibre . . . 

 Fat 



± 

 Per cent. 



0.6 



7.7 



7.2 



25.6 



± 



Per cent. 



0.5 



2.8 

 6.8 



Per cent. 

 0.5 



L6 



31.0 







i 



Calculated by the writer. 





It is evident from these results that deter- 

 minations of the digestibility of concentrated 

 fodders are subject to a somewhat considerable 

 error. When they contain but little of an 

 ingredient, the relative error may be very 

 large, as in the case of the crude fibre of the 

 cottonseed-meal, while, if the ingredient is pres- 

 ent in larger amount, as in the malt sprouts and 

 bran, the relative error is reduced. 



In both Kiihn's and the writer's experiments, 

 however, a second source of uncertainty was 

 discovered in the fact that the same animal 

 may digest the same fodder to a somewhat 

 different extent at different times. The writer's 

 experiments show one unmistakable example 

 of this, and Kiihn's several. 



Now, as stated above, the calculation of the 

 digestibility of a concentrated fodder is based 

 on the assumption of unaltered digestibility of 

 the coarse fodder. If this assumption is not 

 true, the whole of the error thus introduced 

 will, by the method of computation employed, 

 attach to the concentrated fodder. The follow- 

 ing statement shows what very considerable 

 errors may arise from this source, combined 

 with the analytical errors above noted : — 



Possible errors. 





Kiihn's ex- 

 periments. 



Armsby's experiments. 





Bran. 



Malt 



sprouts. 



Cottonseed- 

 meal. 



Dry matter . . . 

 Organic matter 

 Proteine .*'... 

 Crude fibre . . . 

 Fat 



± 



Per ant. 



11.5 



9.6 

 15.4 

 91.5 

 36.1 



± 



Per cent. 



4.3 



5.7 

 10.9 



~ 



± 

 Per cent. 

 4.7 



3.2 



52.4 



