Page:Science vol. 5.djvu/317

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��titDce in computing the composition of large amonnts of fodder from that of small samples. In some recent digeetion experiments mude by the writer at the Wiaconsin agricultural exijeri- (uent-atAtion. a computation was made of the inniieii(>e of tliese analytical errors, with results very similar to tbose arrived at by KiJlui ' in n jiaper on the effect of cooking and other methods of preparation, npoii the digestibility of wheat-bran.

In both coses it was assumed that no mate- rial lose of either fodder or excrement had weurred. In view of the care Uken in the conduct of the experiments, this assumption seems justified. It at least does not magnily the probable error. It was likewise assumed that the sampling was free from error. In the writer's experiments, ntialyses of four samples of the same hay agreed so closely as to justifv the assumption. In tiliort. the computations were confined to the effect of anahjtKol errorn nf>on the results.

With these oxplanatiuns. wc give )>elow a st4itemcnt of the errors to which the several determinations were found to l>e subject: — I'robnble errort. — Hay.

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employed (see alwve), the criors are, so lo speak, concentrated in the by-foddcr. as the following statement shows : —

Probable errort. ~ Bs-fodders.

�� �Kllhn'. «p«ri-

�ArRwbj'a

� �"'"'"■

� � �/Vr,«U.

�IVr^rnl

�DfTuMler ....

� �±0.08

�Oiganic mMter. ..

�±0.1

� � � �± MS

� � � �PVi (ether eilnwt). .

�±2.h

� ��It should, |>erhaps, be added, that the results of a digestion experiment are usually' cxpresse*! in jxT cent of the nmnuut fed. The above results mean, that if. for example, oO% of the proteinc feci was round to have Ijeen digested, the true amount in the writer's experiments Wfta prohablv not less than •I't.a.'ioi nor more than .11.15%.

That tlie probable error appears smaller in the writer's experiments it largely due to the methods of calculation employed. No strict niles ciin he followed in such a computation, but a considerable field must be left for ll)e exercise of good judgment. Kiihn wished to avoid making the error ap|x'ar too small : the writer, with a somewliat different purimse in vi«M. wished to avoid exaggerating it. It is plain that in both exijerimeuls a reasonable degree of accuracy was attained.

Next let us turn iti the results upon by-fod- dcrs. Here, owing to the method necessarily

�� �Kllb>i'.«-

�Anuby-> c

�ip.rt»nl>.

� � �lUlt

� � �Bnn.

�■prool..

� � �±

�±

�±

� � � � �Dry mlT. ..

� �0.5

�0.5

�Organic malter

�(I.R

� � �Proleiiie ....

� � � �Crude fibre. ..

�7.2

�(1.8

�31.0

�Fal

�M.6

� �-

��by lb

��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 l>e very large, as in the case of the crude fibre of the coltonseed-meal, while, if the ingredieut is pres- ent in larger amount, as in the matt apitiuis and bi-an, the relative error is reduced.

In Ijoth 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 ditfeivnt times. The writer's experinienta show one unmistakable example of this, and Kiihn's several.

Now, as slated above, llie calculation of the digestibility of a concentrated fodder is based on the assumption of unaltei-ed digestilnlity of the coai-se fodder. If this assumption is not true, the whole of the error thus iiitroduccil will, by the method of compulation 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 al>ovc noted : — PoNiUe errors.

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�Matt .proou.

� �Dry inalt«r. . . Organic matter - Proleiiie .... Crude fibre. . . Pal

�11. 'l

1).0 1.>.4 1)1.5


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.-..7

10.9

�±

Prrctnl.

4.7

3.2 32.4

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