+--------------+----------------+--------+--------------------------+ | | | | Nitrogen. | | | | +-----+------+------+------+ | | |Duration| In | In | In |Gain +| | Period. | Occupation. |of Test.|Food.|Urine.|Excre-| or | | | | | | |ment. |Loss -| +--------------+----------------+--------+-----+------+------+------+ | | | days |grams|grams |grams |grams | |Fore period |Comparative rest| 5 | 22.0| 18.7 | 1.4 | +1.9 | | | | | | | | | |Working period|Walking 62 miles|{ | | | | | | | per day |{ 5 | 13.2| 21.6 | 1.6 |-10.0 | | | | | | | | | |After period |Rest | 5 | 28.6| 22.0 | 2.2 | +4.4 | +--------------+----------------+--------+-----+------+------+------+ In this case it will be noted that the daily ration was comparatively small, and, further, that during the working period the subject consumed much less proteid than on the resting days. Moreover, when we remember that the total energy value of his diet must have been quite small, it is not at all strange that in the laborious task of walking 62 miles a day he should have temporarily drawn upon his store of body proteid to the extent of 62.5 grams, or 10 grams of nitrogen a day. Such experiences, however, do not by any means constitute proof that in excessive muscular work there is need for the consumption of correspondingly increased quantities of proteid food, or that the energy of muscular work comes preferably from the breaking down of proteid material. Carbohydrate and fat unquestionably take precedence over proteid in this respect, and we may accept as settled the view that in all practical ways carbohydrate and fat stand on an equal footing as sources of muscular energy. Less clear, perhaps, is the question as to how these two radically different types of organic material are utilized by the muscle. It has been a favorite belief among some physiologists that the contracting muscle makes use of only one substance as the direct source of its energy, and that this substance is the sugar dextrose. This view would seemingly imply that fat and proteid must undergo alteration prior to their utilization by the muscle; that, possibly, the carbon of the fat and proteid is transformed into sugar before the muscle can make use of it. So far as fat is concerned, this view is not supported by the facts available, since experiments show that the heat and energy liberated in the utilization of a given amount of fat in muscle work are in harmony with the energy value of the fat; in other words, the fat is apparently burned, or oxidized, directly, without undergoing previous