[CHAPTER XLV.]
TUBERCULOSIS.
Consumption and other Tubercular Diseases.
Consumption (also called phthisis or phthisis pulmonalis) in the year 1899 caused a recorded death-rate of 1,336, and tubercular diseases of other parts of the body a death-rate of 575 per million of the population. In the same year the chief infectious diseases, including small-pox, measles, scarlet fever, whooping cough, typhus, and enteric fever, and diphtheria, were together responsible for a death-rate of 1,248 per million. In the five years, 1861-65, the mean death-rate from consumption was 2,527 per million, so that a reduction of nearly 50 per cent. has apparently occurred. Notwithstanding this great decline, consumption and other consumptive diseases, which may together be classed under the name tuberculosis, still cause more deaths than all the acute infectious diseases put together. Its importance is emphasised by the fact that between the ages of 20 and 45, one-third of all the deaths of males, and between one-third and one-fourth of all the deaths of females occurring at these ages are due to consumption of the lungs.
Formerly great stress was laid on the hereditary character of consumption. It would appear, however, that what is inherited is simply an increased vulnerability of tissues. Judging by the analogy of other animals it may be said that infants are rarely, if ever, born tuberculous. Bang examined 6,000 head of cattle with the tuberculin test (see page [311]), and found that in calves under 6 months old only 10·7 per cent. reacted, i.e. showed evidence of tuberculosis, between 6 and 12 months old 18·7 per cent., 1 to 2 years 23·2 per cent., and over this age 31·3 per cent. reacted; from which it may be inferred that the infection is nearly always received after birth.
The real cause of tuberculosis was shewn by Koch, in 1881, to be the tubercle bacillus. This is a minute bacillus, the length of which is from a quarter to half the size of a blood corpuscle. These bacilli, obtained from tuberculous growths in the body, Koch was able to cultivate on glycerine agar at blood-heat outside the body. By sub-culturing he obtained pure cultures, and after growing the bacilli for as long as fifty-four days, he inoculated various animals, producing tuberculosis in every case, while in similar check experiments in which all the conditions were the same, barring the absence of bacilli, no tuberculosis resulted.
The tubercle bacilli are easily distinguished from most other bacilli by the fact that after being stained by aniline dyes, such as carbol-fuchsin, the colouration is not removed when the preparation is soaked in dilute acid. By this means the presence of tubercle bacilli in the sputum (expectoration) of a phthisical patient is easily discovered, and a valuable means of early recognition of the disease secured. This is most important, as in its early stages consumption is an easily curable disease. Tubercle bacilli are discharged from the lungs in consumption of the lungs, from the bowels in consumption of the bowels, and so on. Hence the essential necessity for disinfecting these discharges. Such discharges while in a moist condition have, unless they are actually swallowed, little or no capacity for evil. It is when they become dry that they become dangerous. Thus the expectoration of a consumptive patient spat on to the floor or deposited in a pocket handkerchief is, so long as it remains moist, perfectly innocuous. What is evaporated from the wet surface is simply steam, harmless as the steam escaping from the domestic tea-kettle. But when it becomes dry, then comes danger. Dust is formed, which contains the living tubercle bacilli, and with the mere shaking of the handkerchief or the disturbance of the dust on the floor these are inhaled, and often cause consumption. The person thus infected may be a new patient. Often also it is the consumptive patient who is thus re-infected. Consumptive patients tend to recover. But if the patient’s disease is daily recruited by fresh doses of the tubercle bacilli inhaled with the dust of previous expectoration, fresh centres of disease are produced, and thus the patient is unwittingly helping to cause his own death.
The infectious character of tuberculosis has been long suspected. In the 18th century, in Naples, there were enactments insisting on the isolation of consumptive patients and disinfection of their furniture, books, etc. We now know, however, that these were counsels of panic, and that for practical purposes the infection may be regarded as confined to the sputum. The expired breath is free from infection except during coughing. That the sputum is infectious can be easily proved by feeding guinea-pigs or the domestic fowl on it. These rapidly become affected by generalised tuberculosis. The simple character of the precautions against infection which are required may be gathered from the following copy of a card which is given to consumptive patients in Brighton:—
Precautions for Consumptive Persons.
Consumption is, to a limited extent, an infectious disease. It is spread chiefly by inhaling the expectoration (spit) of patients which has been allowed to become dry and float about the room as dust.
Do not spit except into receptacles, the contents of which are to be destroyed before they become dry. If this simple precaution is taken, there is practically no danger of infection. The breath of consumptive persons is free from infection.