Some bacteria can cause infections, but others are harmless or even helpful to the human body.
As regards infections, it is not to be supposed that our knowledge of these maladies has been advanced by pathology and bacteriology only.
It is on clinical grounds that beriberi, scarlet fever, measles, &c., are recognized as belonging to the same class, and evolving in phases which differ not in intimate nature but in the more superficial and inessential characters of time, rate and polymorphism; and the impression is gaining strength that acute rheumatism belongs to the group of the infections, certain sore throats, chorea and other apparently distinct maladies being terms of this series.
As regards pulmonary disease, pneumonia has passed more and more definitely into the category of the infections: the modes of invasion of the lungs and pleura by tuberculosis has been more and more accurately followed; and the treatment of these diseases, in the spheres both of prevention and of cure, has undergone a radical change.
Wright and his co-workers to control the treatment of bacterial infections by vaccines; that is, by injections of varying amounts of a dead culture of the corresponding bacterium.
Such serums are injected subcutaneously in diphtheria, tetanus, streptococcic infections, plague, snake-poisoning, cholera and other similar diseases.
In areas where Jenner's techniques were available, infections fell, and when inoculation became mandatory, they plummeted.
Ludwig Brieger then discovered the toxins of certain infections; and Emil A.
In the tropics, as well as in Europe, such methods and such researches threw new light upon the causes and paths of the terrible infections of these climates.
Coincidently therewith, the hope of neutralizing infections by fortifying individual immunity has grown brighter, for it appears that immunity is not a very radical character, but one which, as in the case of vaccination, admits of modification and accurate adjustment in the individual, in no long time and by no very tedious methods.
When, leaving the infections, we look for evidence of progress in our knowledge of more or less local diseases, we may begin with the nervous system.
Of such probably are the toxins and antitoxins of certain infections, which, anchoring themselves not by any means indiscriminately, but to particular and concerted molecules, by such anchorage antagonize them or turn them to favourable or unfavourable issues.