five miles; during the fifth period they did their usual work. The quantities of urea excreted during the five periods are tabulated as under,

Liebig's explanation of the results disclosed in the above tables is, that they demonstrate that muscular exertion causes an augmentation of urea, though the increased excretion does not take place immediately, but at a subsequent period. Thus it will be noticed, that during the second period, though both individuals were at rest, the excretion of urea was increased, conformably, no doubt, as we have hinted, that the tissues were not operated on by the increased quantity of oxygen circulating in the blood, until the supplementary amount of proteids which it contained were reduced to normal excreta. This view is also confirmed by the experiments of Fick and Wislicenus, in whom also the amount of urea was markedly increased after the exertion.

In Dr Parkes' cases, again, during the third period, the amount of urea excreted was the same as in the first; it increased markedly during the fourth; while in the fifth period it was higher than during the first and third periods. It is particularly interesting to notice that during the second period the weight of the body decreased, during the third it increased; decreased considerably during the fourth, and was restored to its original weight during the fifth period. The loss of weight suffered during a long march by both individuals was considerable, both with ordinary diet and nitrogenous diet. In the case of S., the loss of weight during this period amounted to 5 lbs. and 4 lbs.; in the case of B., 42 lbs. and 14 lb. The reason for this loss of weight cannot be doubted. Both individuals may have lost fat by a greater consumption of oxygen during the severe work; but the greater part of the loss was undoubtedly water,-not, indeed, liquid water that could be replaced by drinking, but water that was combined in the muscles and tissues, and had been set free in consequence of the metamorphosis or consumption of muscular substance. The slow restoration of the bodily weight and the necessary co-operation of the food, prove that the tissues which, in their natural condition, had retained the water eliminated, were altered in their character; four days elapsed in the case of S. and B. before they had again acquired their original weight.

Of the total quantity of force capable of being generated in the animal body, a portion is applied in performing interior work, comprising (a), all involuntary motions of the blood and respiration, &c., (b), for working up the food into those substances which serve

for the construction and restoration of organs; and it is only the portion remaining after these operations have been performed that is available for the performance of external work.--(Liebig.)

Considering the very opposite conclusions arrived at, such as those presently to be noticed by Dr Flint, and the discrepancies of opinion among physiologists, may it not be suggested that muscular tissue breaks down. in a particular order-the less stable first-and that experiments to be reliable must be prolonged for certain periods?

Dr Flint's interesting and highly important observations are as follow:-Some time ago he had an opportunity of examining the urine of a gentleman who performed the pedestrian feat of walking 100 miles in twenty-one hours and thirty-nine seconds. On this occasion, his examination of the urine led Dr Flint to form conclusions opposed to doctrines recently gaining ground. He found the urea so considerably in excess, presuming on ordinary diet having been partaken of, as to indicate that it resulted from increased muscular exertion. Certain data being wanted to form reliable conclusions, Dr Flint waited for a further opportunity of testing the matter, and which soon presented on Mr Weston, the pedestrian referred to, undertaking to walk 400 miles in five consecutive days, on one of which he was to have walked 112 miles in twenty-four consecutive hours. Mr Weston's diet was in no way interfered with. That which he was about to eat was weighed, that left likewise weighed, and the difference estimated as consumed. The fæces and urine were carefully weighed and analysed. Mr Weston underwent but little training; he ate well,

but it is noteworthy that he habitually excreted a more than average amount of urea, the quantity being 628 grains, being 33 per cent. more than Dr Parkes' estimate. Mr Weston's weight was only 120 lbs., and as the excretion of urea is in the ratio of 3.5 grains per lb., 420 grains would represent the normal quantity. Mr Weston walked as follows:-80 miles the first day, 48 the second, 92 the third, 57 the fourth, 401 miles on the fifth day, in all 317 miles in five consecutive days, thus losing his wager, it will be noticed. The elimination of urea was 722 grains per diem on an average. Five days afterwards he took but little exercise, though, as in the cases already referred to, his excretion of urea amounted on a daily average to not less than 727 grains.

Dr Flint remarks, that during the five days of violent exercise Mr Weston consumed 1174 grains of nitrogen, in which time he eliminated in his urine and fæces 1808 grains of nitrogen, leaving a difference of 634 grains of nitrogen which must have been derived from the waste of muscular tissue. Estimating the percentage of nitrogen in the muscular tissue at 3 per cent., 634 grains would represent a loss of 21 127 grains, or 3018 lbs. of muscular tissue. The actual loss was 3:450 lbs., allowing 0.43 lb. unaccounted for, which it is suggested might be fat or water. During the five days' rest succeeding the walk, Mr Weston gained in weight 4.5 lbs., and retained in his system an amount of nitrogen equivalent to 1.1 lb. of muscle.* Dr Flint arrived at the following conclusions:-" If these facts be accepted, and leaving the widest margin for error in the estimate, they cannot involve any considerable * British and Foreign Med. Chir. Rev., and Practitioner.

error, it is impossible to come to any other conclusion than that excessive and prolonged muscular exertion increases enormously the excretion of nitrogen, and that the excess of nitrogen discharged is due to an increased disassimilation of the muscular substance; and it is to be remembered that the experiments on which this statement is based were made with a diet regulated solely by the taste of the individual." This question, then, may at least be said to be sub judice.

How does it affect the pathology and therapeutics of gout and rheumatism? It is admitted that urea, carbonic acid, water, and ammonia, &c., are the results of the ultimate oxidation of effete tissue; but it does not follow that these are the results of direct oxidation; nay, it is rather more probable that they are the results of a series of chemical evolutions. If they are the results of oxidation, and if in certain states, as under the influence of great bodily exertion, a relatively larger amount of oxygen is consumed by the body, the conclusion is irresistible that increased tissue metamorphosis must be manifested in increased excretion, if not in urea, at least in some of the other excretions, such as carbonic acid and water. According to Dr Smith, carbonic acid is much increased by muscular exertion.

It is not absolutely contended, then, that urea is directly formed in the depths of the tissues, as the researches of Dr Parkes and others render it highly probable that the liver is the organ by which urea is elaborated from less oxidised material presented to it.*

In the "Centralblatt für Medizin Wissenschaft," Dr Cyon, of St Petersburg, has published the result of researches made by him on this subject. Blood withdrawn from the carotid arteries of dogs was rapidly defibrinated; a portion of it was placed in an apparatus by which it was propelled by me