This explanation of the above-mentioned phenomena does not damage the probable hypothesis that every calorie consumed within the organism gives the same work value, and that only the external expression of work changes; it seems for the present, therefore, to be the most plausible.

For every individual there is a day's work, varying within certain limits, which is his normal work, and which is an essential condition of the maintenance of his healthy functions and general well-being. I would remark in passing that such normal work does not exclude, but probably rather causes, a moderate daily fatigue.

Work which is short of this very varying amount for each individual is under-work, and in the long run produces functional changes and illnesses which at all ages are much commoner phenomena than the results of over-strain. A child living a sedentary life suffers in his whole psychical and other development, is especially weak in muscle, weak in heart, weak in nerve, anaemic and delicate throughout. An adult leading a sedentary life shows similar symptoms, readily falls into "apathy," is an easy victim to neurasthenia, obesity, gout or diabetes, suffers from haemorrhoids, constipation and more or less definite symptoms in connection with nearly all the systems of the body.

In contrast to the results of a too inactive way of living stand the results of over-work, which results we group under the term over-strain, acute or chronic. It is, as already mentioned, a somewhat rare phenomenon, and, at least in Sweden, is especially rare among physical workers. Acute over-strain seems to be commonest among troops on the march and in enthusiastic sportsmen; the chronic form (in time of peace) is most often met with in the latter.

* Other writers (Marey, Edwards, Gad and Heymons, Carovallo and Weiss and others) find that a temperature of about 38° C. is the most favourable for muscle work in man.

Under the term "physical over-strain" one might include all pathological phenomena produced by too extensive, too strong, or too long-continued physical work. The term would then include many conditions which arise in a purely mechanical way. One might, for example, reckon among the results of over-strain dilatation, rupture, or paralysis of the heart, dilatation or rupture of blood vessels, rupture or over-strain of muscles, hernia, sprains, dislocations, and even certain fractures.

In speaking of acute and chronic physical over-strain the physician seldom thinks of any of the above conditions, except those which directly concern the heart muscle and nerves. Otherwise the clinical picture of over-strain which rises before him includes many symptoms, many of which are certainly of a mechanical nature, but most of which, especially in acute over-strain, have chemical causes, and to some extent show an unmistakable likeness to purely toxic symptoms. Without paradox one may support the view that physical overstrain is partly an intoxication, which is explained by the fact that moderate physical work, like certain substances, has an exciting effect, while excessive effort, like the same substances in larger doses, produces symptoms of depression. A quick and not too long walk has a slight exciting effect, which by its influence on the heart, on respiration, on the mind, on the feeling of strength, and on the whole nervous system acts in a very similar way to other forms of excitation; after forced marching marked depression arises.

The symptomatic picture of acute strain varies much according to the intensity of the physical exercise.

Short, violent strain is known chiefly by symptoms from the heart and respiratory apparatus; these show themselves before symptoms of muscle fatigue become marked.

If, e.g., some one climbs a small incline quickly, when he arrives at the top he suffers chiefly from dyspnoea. The respiration is "panting," its speed as much as twenty or even thirty a minute, the volume of inspiration and expiration almost reaches the amount of the vital capacity, and all the respiratory muscles arc brought into play.

It is doubtful whether even in this state of things the blood in the veins of the systemic circulation is more rich in oxygen than usual (see p. 120). For if we examine the heart we find that the right side especially has been over-strained by doing the increased amount of work necessary.

The breadth of cardiac dulness is increased as a result of the inability of the right ventricle to complete systole, and of its distension by blood. The pulse is quick, small, and not seldom uneven, while an occasional beat is absent. On continued examination, while the test patient recovers from the strain, one is able to estimate how the cardiac dulness diminishes in breadth, and how the pulse by degrees becomes fuller and more even, in proportion as the panting respiration and the pulmonary circulation return to normal and the left ventricle receives a full blood supply. In a strong normal individual such a slight excess is followed by no continued injurious results. But violent strains, relatively or absolutely too great, may produce dilatation, with incompetence and other results. Rupture of the heart, which may be fatal immediately or only after a day or two, or paralysis of the heart are not unknown phenomena after such excesses.

After somewhat less intensive, but more continuous and severe, physical exercise, for example after many hours' walking, there arise in acute over-strain lesser symptoms from the circulatory and respiratory apparatus than those of fatigue, with accompanying symptoms from muscles and nerves.

After excessive work one finds in the tired muscles, e.g., the leg muscles after forced marches, a condition which strongly resembles acute myositis. They are the seat of spontaneous pains, are tender on pressure, and on palpation they seem doughy and swollen and of diminished elasticity. There is little doubt that the marked hyperaemia of the motor apparatus after too severe strain may cause inflammation. Many doctors consider that both acute myositis, acute tenosynovitis, and acute synovitis may he the result of such excess.

Modern neurologists - I am thinking particularly of Oppenheim - express the same opinion with regard to neuritis.

It is after such fatigue that we often find a slight temporary albuminuria.

Tremor and cramp in the over-strained muscles are common symptoms - after marches particularly gastrocnemius cramp.

When fatigue becomes extreme it spreads by degrees to the cerebro-spinal nervous system. Movements become weak and uncertain; the temporarily increased psychic irritability gives place to loss of will-power and sluggishness, and finally the patient falls into a deep, heavy sleep.

Chronic over-strain also is easily felt by the heart, skeletal muscles, and nerves. But there are besides disturbances in the general nutrition.

We find two common affections of the heart in such cases - hypertrophy, with or without previous dilatation, and cardiac neurosis, both most common among certain classes of sportsmen.

In the skeletal muscles we find also two affections - atrophy as a result of over-strain, and occupation or co-ordination neuroses. Both arise as the result of one-sided muscle work, i.e., continuous excessive work for certain groups of muscles.

Atrophy due to over-strain is rare; it may sometimes arise in labouring men, but more often in sportsmen. A weaver, who extends his arm 20,000 times a day, gets atrophy of triceps (Oppen-heim); Lennmalm in Stockholm observed atrophy of the right calf muscles in a sleighing amateur using the long, narrow light sledge used in Scandinavia, propelled in the same way as a child's scooter.

Co-ordination or occupation neuroses with tremor, spastic, or paralytic symptoms from the over-strained muscle groups are far more common (in writers, pianists, dancers, etc.); all of us with experience have seen many of these.

Continued excess of more widespread muscle work causes the more or less developed picture of neurasthenia. Such patients are often very anaemic, and often show considerable loss of flesh below their normal weight.