If any one doubts the importance of an acquaintance with the principles of physiology, as a means to complete living, let him look around and see how many men and women he can find in middle or later life who are thoroughly well.  Only occasionally do we meet with an example of vigorous health continued to old age; hourly do we meet with examples of acute disorder, chronic ailment, general debility, premature decrepitude.  Scarcely is there one to whom you put the question, who has not, in the course of his life, brought upon himself illnesses which a little information would have saved him from.  Here is a case of heart-disease consequent on a rheumatic fever that followed reckless exposure.  There is a case of eyes spoiled for life by over-study.  Yesterday the account was of one whose long-enduring lameness was brought on by continuing, spite of the pain, to use a knee after it had been slightly injured.  And to-day we are told of another who has had to lie by for years, because he did not know that the palpitation he suffered under resulted from overtaxed brain.  Now we hear of an irremediable injury which followed some silly feat of strength; and, again, of a constitution that has never recovered from the effects of excessive work needlessly undertaken.  While on every side we see the perpetual minor ailments which accompany feebleness.  Not to dwell on the pain, the weariness, the gloom, the waste of time and money thus entailed, only consider how greatly ill-health hinders the discharge of all duties—­makes business often impossible, and always more difficult; produces an irritability fatal to the right management of children; puts the functions of citizenship out of the question; and makes amusement a bore.  Is it not clear that the physical sins—­partly our forefathers’ and partly our own—­which produce this ill-health, deduct more from complete living than anything else? and to a great extent make life a failure and a burden instead of a benefaction and a pleasure?

Nor is this all.  Life, besides being thus immensely deteriorated, is also cut short.  It is not true, as we commonly suppose, that after a disorder or disease from which we have recovered, we are as before.  No disturbance of the normal course of the functions can pass away and leave things exactly as they were.  A permanent damage is done—­not immediately appreciable, it may be, but still there; and along with other such items which Nature in her strict account-keeping never drops, it will tell against us to the inevitable shortening of our days.  Through the accumulation of small injuries it is that constitutions are commonly undermined, and break down, long before their time.  And if we call to mind how far the average duration of life falls below the possible duration, we see how immense is the loss.  When, to the numerous partial deductions which bad health entails, we add this great final deduction, it results that ordinarily one-half of life is thrown away.