Experiments 2 & 3.-In both these experiments the proportion of nitrogenous substance in the food was very large; the relation of non-nitrogenous to one of nitrogenous substance being in Exp.2 little more than half, and in Exp. 3 little more than one-third as much as is usual in the recognized good fattening food of the animal. In Exp. 2 the food consisted of bran, bean and lentil-meal, and Indian-meal, each given separately, and ad libitum; and in Exp. 3 of an equal mixture of bean and lentil-meal only, given ad libitum.

Experiments 4 & 5.-In Exp. 4 the food consisted of Indian meal only, and in Exp. 5 of barley-meal only, in each case given ad libitum. Barley-meal is undoubtedly the most approved staple fattening food of the pig; and the result was, that in both these experiments the proportion of non-nitrogenous to nitrogenous substance in the food was very nearly, though rather higher than, the average in that which is recognized as the most appropriate fattening food of the animal.

Experiments 6, 7, 8, & 9.-The peculiarity of this series was, that the food contained less ready-formed fat than was the case in either of the other experiments, and that a large proportion of the non-nitrogenous substance supplied was in the form of either pure starch, pure sugar, or both. In Exps. 6, 7 & 8, a fixed quantity of lentil-meal and bran (averaging nearly 3 lbs. lentil-meal and about 9 ounces bran) was given per head per day, and, in addition, in Exp. 6 sugar, in Exp. 7 starch, and in Exp. 8 sugar and starch, each separately, ad libitum. In Exp. 9 lentil-meal, bran, sugar, and starch were each given separately, ad libitum.

The figures given in the Table show that the increase in weight was in no case less than 50, and in several nearly, and in one more than 100 per cent., upon the original weight of the animals, the amounts ranging from 513 to 68.9 per cent. when the experiment extended over eight, and from 854 to 106.8 per cent. when it extended over ten weeks.

The determined or estimated amount of fat stored up in the increase was also in all cases very large, amounting to 63 per cent. of the total increase in Exp. 1, in which it was experimentally determined, and calculated to be even more than this in several of the other cases. The tendency to error in the calculations would, however, be to give the proportion too low in Exps. 6, 7, 8 & 9, which were conducted over a period of ten weeks, and in which the proportion of increase upon the original weight was very high, and to give it too high in Exps. 2, 3, 4 & 5, conducted only over eight weeks, but more especially in Exps. 2 & 4, in which the proportion of increase upon the original weight was comparatively small. The rang

of the probable error of calculation here indicated is, however, not such as in any degree to throw doubt upon the validity of any conclusions which will be drawn from the indications of the figures as they stand.

It is seen that, of the determined or estimated total fat stored up in the increase, the proportion which could possibly have been derived from the ready-formed fat of the food, even supposing the whole of that supplied had been assimilated, was so small as to leave no doubt whatever that a very large proportion of the stored-up fat must have been produced from other constituents than the ready-formed fatty matter of the food. According to the figures given in the Table, the proportion of fat which must have been so produced, ranged from about twothirds to about eight-ninths of the total amount stored up.

Assuming it, then, to be established beyond doubt that there was a very large formation of fat within the body from other constituents than the fatty matter of the food, the questions arise, whether this large amount of produced fat could possibly have been derived from the nitrogenous constituents of the food? or whether it must of necessity have had its source, in greater or less proportion, in the carbo-hydrates at the same time supplied? The results adduced afford conclusive evidence on this point also.

The figures show that, after deducting from the total amount of nitrogenous substance consumed for the production of 100 lbs. of increase in live-weight the small amount estimated to be stored up in the increase, there remains a very large proportion available, it may be, for the production of fat with other products.

If we next compare the amount of carbon in the estimated produced fat with the amount contained in the nitrogenous substance of the food not stored up as increase, minus that contained in the urea which would be one of the final products of the breaking up of this nitrogenous substance (or its equivalent given off), the result shows in some cases an excess, and in others a deficiency, of carbon possibly available from the nitrogenous constituents of the food, compared with that required for the formation of the fat estimated to be derived from other constituents than the ready-formed fat in the food.

Reckoned to the standard of 100 carbon in the estimated produced fat, it is seen, as shown in the two bottom lines of the Table, that in Exps. 1, 2 & 3, in which the proportion of non-nitrogenous to nitrogenous substance in the food was (especially in Exp. 3) considerably less than in such food as experience has shown to be the most appropriate in the fatten

stance was in considerable excess over the amount and proportion usually supplied-there was, according to the calculation, more than sufficient carbon possibly available from the nitrogenous substance of the food for the formation of the fat estimated to be produced.

In Exps. 4 & 5, however, in which the relation of the nonnitrogenous to the nitrogenous substance in the food was much more nearly that in the usual food of the well-fed fattening pig, it is reckoned that there was about 40 per cent. of the carbon of the produced fat which could not possibly have been supplied from the nitrogenous constituents of the food.

In the other experiments (Nos. 6, 7, 8 & 9), in which again the proportion of the non-nitrogenous to the nitrogenous constituents of the food was lower than usual (though not so much so as in Exps. 1, 2 & 3)-in which, in fact, the nitrogenous constituents were in excess-there was still a considerable proportion of the carbon of the produced fat which the nitrogenous constituents of the food could not possibly have supplied.

It is hardly necessary to point out that, according to the mode of illustration we have adopted, the figures show not only the utmost proportion of the carbon of the stored-up fat which could possibly have had its source in the nitrogenous substance of the food, but even notably more than could possibly have been so derived. Thus, to say nothing of other considerations, it has been assumed for simplicity of illustration, and granted for the sake of argument, that the whole of the ready-formed fatty matter of the food contributed to the fat stored up, that the whole of the nitrogenous substance of the food not stored up as increase would be perfectly digested and become available for the purposes of the system, and that in the breaking up of the nitrogenous substance for the formation of fat no other carboncompounds than fat and urea would be produced. It is obvious, however, that these assumptions are in part improbable, and in part quite inadmissible, and that the tendency of each of them is to show too large a proportion of the produced fat to have been possibly derived from the nitrogenous constituents of the food.

The amount of fat necessarily derived from other sources than the nitrogenous constituents of the food must therefore be greater than our mode of estimate can indicate; and it is obvious, from the figures given in the Table, that the less the excess of nitrogenous substance in the food, the greater was the proportion of produced fat which must necessarily have had its source in the carbo-hydrates of the food, and that, at any rate in those cases in which the proportion of non-nitrogenous to Phil. Mag. S. 4. Vol. 32. No. 218. Dec. 1866. 2 G

nitrogenous constituents supplied was the more nearly that occurring in the admittedly most appropriate fattening food of the animal, the proportion of the fat which must necessarily have been derived from the carbo-hydrates was very large, even allowing all that was possible to have been produced from the nitrogenous substance of the food.

That, nevertheless, fat may be produced in the animal body at the expense of nitrogenous substance, in greater or less degree according to the character of the animal and of the food, not only chemical and physiological considerations, but direct experimental evidence would lead us to conclude. Indeed we

have, in former papers already referred to, called attention to the fact that the results of our experiments with fattening animals, when carefully considered, afford evidence in favour of such a conclusion. To discuss the point satisfactorily on the present occasion, by the aid of figures, would, however, unduly extend the limits of our paper.

But, as indicating the bearing of the results referred to, it may be stated, in passing, that in numerous cases, otherwise comparable, but in which the amount and proportion of the nitrogenous constituents consumed varied very greatly, the results clearly showed that neither the amount of food consumed, nor the amount of increase in live-weight produced, bore any direct relation to the amount of nitrogenous substance supplied. On the other hand, both the amount of food consumed and the amount of increase produced bore a very close relation to the supply of digestible non-nitrogenous constituents, and even a closer relation still to the amount of total digestible dry organic substance (that is, nitrogenous and nonnitrogenous taken together); whilst, so far as could be judged from careful observation, the proportion of nitrogenous to nonnitrogenous substance (fat) in the increase did not vary in anything like a corresponding degree with the variation in the proportion of the nitrogenous and non-nitrogenous constituents in the food. The animals consuming excessive amounts of nitrogenous substance did, indeed, show a greater tendency to increase in frame and flesh; but they nevertheless became fat. It would appear that the excess of nitrogenous substance had acted vicariously in defect of a greater supply of the non-nitrogenous constituents, contributing material not only to meet the respiratory exigencies of the animal, but also for the production of fat.

The main conclusions in regard to the sources of the fat of the animal body to which the evidence adduced has led, may be briefly stated as follows:

vora fattened for human food must be derived from other substances than fatty matter in the food.

2. That when fattening animals are fed upon their most appropriate food, much of their stored-up fat must be produced from the carbo-hydrates it supplies.

3. That nitrogenous substance may also serve as a source of fat, more especially when it is in excess and the supply of available non-nitrogenous constituents is relatively defective.

LXII. On the Influence of Magnetization on the Length and the Resistance of Iron Bars. By W. BEETZ*.

WIEDEMANN+ and Buff ‡ have both expressed opinions as

to the molecular actions which occasion a lengthening in an iron bar when it is magnetized. From these actions we may expect on the one part a lengthening, on the other part a shortening of the bar. For it may be supposed

(1) On the theory of magnetic fluids, that a shortening of the bar occurs in consequence of the mutual attraction of molecules which have become magnetic.

(2) On Ampère's theory, that the parallel currents attract each other, whereby the bars are shortened.

(3) That the molecular magnets set with their long axis parallel to the axis of the bar, and thus produce a lengthening of the bar, a view which De la Rive§ has expressed, and to which Tyndall and Buff adhere.

(4) That, by magnetizing, a mechanical pull is exerted on some parts of the bar, which lengthens it, as was observed by Wertheim T.

(5) That the bar was previously twisted or bent, and that magnetization stretches it by removing this.

In fact, both a lengthening and a shortening action have been observed in the magnetization of iron bars: Joule**, Wertheim, and Buff have undoubtedly shown a lengthening, and Tyndall++ has even demonstrated it by a lecture-experiment; Joule has further shown that, instead of a lengthening, there is a shortening if the bars or wires are under a strong strain.

From the supposed molecular actions, conclusions may be drawn

Translated from Poggendorff's Annalen for June 1866.

† Lehrbuch des Galvanismus, vol. ii. p. 457.

Liebig's Annalen, Supplementary volume iii. p. 136. § Ann. de Chim. et de Phys. ser. 3. vol. xxvi. p. 158.

|| Cosmos, vol. xxiv. p. 719.

Poggendorff's Annalen, vol. lxxvii. ** Phil. Mag. S. 3. vol. xxx. p. 76.