In my fourth Lecture I gave an Etiological analysis of those states of disease assembled under the following six headings in the Registrar-General's Reports of the deaths in London. (Report of the deaths in London registered in the 21st week of each of the ten years 1848-57, the Report current at the time the notes for these Lectures were made.)

1. Typhus, typhoid and other forms of continued fever.

2. Apoplexy and Paralysis.

3. Heart diseases and Pericarditis.

4. Rheumatism and Gout.

5. Bronchitis.

6. Atrophy and Debility.

I demonstrated that, when we analyse the natural history of any disease, we find that the principal factors of its essential cause, of its predisposing causes, and of the causes of i s fatality fall under one of the three headings: - 1. Conditions of life. 2. Coetaneous diseases. 3. Vestiges of Disease.

I showed, not only theoretically but from actual observations made by others^ as well as by myself, how the organism becomes damaged by these Vestiges of Disease - how the vital force becomes defective through these Vestiges, how this defective state of the vital force becomes the essential cause and the predisposing cause of disease; and how the Vestiges of one disease become the causes of fatality in whole families of other diseases.

I endeavoured to prove, by an array of facts, that the vestiges of disease become causes of fatality in other diseases principally in two ways: -

1. By destroying those modes of matter and their correlation of conditions upon which the existence of the vital force in its normal condition depends, thus producing excessive defect of the vital force.

2. By producing excessive defect in the condition of some part of the organism, occupying the position, at the time of an essential instrument in the processes of life, and thus causing the organism to break down at this its weakest part.

I pointed out that in the large majority of deaths from disease, the fatality is due, not to the disease itself, but to the vestiges of some pre-existent disease, operating in one or other of the above ways.

In illustration of this great fact, I have set forth the course of events by which the vestiges of disease, passing under the names of anaemia and fatty degeneration, become the actual causes of a large number of the deaths registered under the following names: -

Tabes mesenterica, croup, measles, hydrocephalus, whooping-cough, dentition, convulsions, apoplexy, paralysis, delirium tremens, intemperance, angina pectoris, diseases of the heart, pneumonia, diarrhoea, mortification, influenza, peritonitis, childbirth, bronchitis, jaundice, liver disease, kidney disease, and some others.

As an indication of the insidious way in which the deadly influence is exerted by these states - anaemia and fatty degeneration - (which are only examples of a class) - I called attention to the fact that their names do not appear in the bills of mortality. (See Anaemia and Fatty Degeneration.)