waste-products of combustion, will not be so easily produced.

In a man in perfect "condition," the products of excretion which are removed from the body by the eliminating organs will not be the same as before training, for the tissues, the dissimilation of which gives rise to them, will be different. The lungs will eliminate less carbonic acid for an equal quantity of work, and will no longer eliminate certain little-known gaseous products, which result from the combustion of materials which have been too long retained in the body. The skin will no longer exhale the volatile fatty acids, the smell of which is sometimes so marked in persons of sedentary life. The kidneys, after intense muscular work, will no longer eliminate the excess of urates and other nitrogenous waste-products which are found in the urinary deposits, and which are so abundant in untrained persons attacked by stiffness.

Hygienists have long pointed out the fact that all the excretions vary in a striking manner in different individuals, according to their mode of life. The exhalations of human beings have even a different smell, according as they emanate from a man who is in the habit of performing muscular work, or a man who leads a very sedentary life. The odour of a prison has been said to differ characteristically from that of a barrack. Both result from volatile products eliminated by the lungs and skin of a great number of men crowded together; but the men of one class have led an inactive life, the others have been in continual activity.

We may certainly say that the system of the trained person has undergone sufficiently profound changes to make of him a being physiologically very different from another who has not undergone the same training. His conformation is different, the structure of his tissues has changed. His organs have undergone a transformation and their working is no longer the same.

The person modified by training, and he who has led an exceedingly sedentary life, must be considered, from

a standpoint of observation and experiment, as very different physiological units. If we place them in identical conditions, in which they are submitted to modifying agents, they will not react in the same manner. Work, in especial, will modify in a different manner the working of all their organs. For the same number of kilogrammes of work done in a given time, we shall not observe in them a like quickening of pulse and respiration; the air they expire will not contain the same quantity of carbonic acid; their urine will not eliminate the same quantities of uric acid.

Hitherto insufficient notice has been taken of the profound changes produced in the results of work by the transformation undergone by the organism in becoming habituated to muscular exercise. The greater number of the observations made on men to estimate the products of excretion resulting from work, are fallacious, owing to the fact that, the influence of this important factor has not been taken into account, the condition of training of the subject.

This is doubtless the cause of the great differences amongst authors who have examined the effect of work on the excretions, especially on the urine.

PART IV.

THE DIFFERENT EXERCISES.

PHYSIOLOGICAL

CLASSIFICATION OF EXERCISES

VIOLENT EXERCISES-EXERCISES OF STRENGTH -EXERCISES OF SPEED-EXERCISES OF ENDURANCE-MECHANISM OF DIFFERENT EXERCISES.