Finally, in 1905—­after Metchnikoff had prepared the way by succeeding in carrying syphilis from man to monkey, and Lassar, by inoculation, from monkey to monkey—­Fritz Schaudinn made his great discovery of the protozoal Spirochoeta pallida (since sometimes called Treponema pallidum), which is now generally regarded as the cause of syphilis, and thus revealed the final hiding place of one of the most dangerous and insidious foes of humanity.[224]

There is no more subtle poison than that of syphilis.  It is not, like smallpox or typhoid, a disease which produces a brief and sudden storm, a violent struggle with the forces of life, in which it tends, even without treatment, provided the organism is healthy, to succumb, leaving little or no traces of its ravages behind.  It penetrates ever deeper and deeper into the organism, with the passage of time leading to ever new manifestations, and no tissue is safe from its attack.  And so subtle is this all-pervading poison that though its outward manifestations are amenable to prolonged treatment, it is often difficult to say that the poison has been finally killed out.[225]

The immense importance of syphilis, and the chief reason why it is necessary to consider it here, lies in the fact that its results are not confined to the individual himself, nor even to the persons to whom he may impart it by the contagion due to contact in or out of sexual relationships:  it affects the offspring, and it affects the power to produce offspring.  It attacks men and women at the centre of life, as the progenitors of the coming race, inflicting either sterility or the tendency to aborted and diseased products of conception.  The father alone can perhaps transmit syphilis to his child, even though the mother escapes infection, and the child born of syphilitic parents may come into the world apparently healthy only to reveal its syphilitic origin after a period of months or even years.  Thus syphilis is probably a main cause of the enfeeblement of the race.[226]

Alike in the individual and in his offspring syphilis shows its deteriorating effects on all the structures of the body, but especially on the brain and nervous system.  There are, as has been pointed out by Mott, a leading authority in this matter,[227] five ways in which syphilis affects the brain and nervous system:  (1) by moral shock; (2) by the effects of the poison in producing anaemia and impaired general nutrition; (3) by causing inflammation of the membranes and tissues of the brain; (4) by producing arterial degeneration, leading on to brain-softening, paralysis, and dementia; (5) as a main cause of the para-syphilitic affections of general paralysis and tabes dorsalis.

It is only within recent years that medical men have recognized the preponderant part played by acquired or inherited syphilis in producing general paralysis, which so largely helps to fill lunatic asylums, and tabes dorsalis which is the most important disease of the spinal cord.  Even to-day it can scarcely be said that there is complete agreement as to the supreme importance of the factor of syphilis in these diseases.  There can, however, be little doubt that in about ninety-five per cent. at least of cases of general paralysis syphilis is present.[228]