In its tendency syphilis is constantly progressive and destructive, although it often behaves in a capricious manner, sometimes when under efficient treatment and generally when treatment is inefficient. It is usually more virulent in the dissipated and those who are weakened by inheritance or poor constitutions, or by other disease. One reads in literature on the subject about the malignancy of some cases and the benignancy of others. Some cases seem to have a malignant aspect, while others run an unusually mild course, so much so as to raise the question whether the patient had syphilis. As far as the nature of the parasitic cause is understood, this would depend on differences in the make-up of the individual rather than in the actual virulence of the germ. In the extremes of life individuals are more susceptible. When implanted upon a tuberculous constitution it sometimes renders the tuberculous lesions more active; whether it acts as a mixed infection is not definitely known. Tuberculous lymph nodes frequently break down during the course of secondary syphilis, and consumptive patients grow rapidly worse. Syphilis, like alcohol, tends to play havoc with the bloodvessel walls, and their combined effects in this direction are greatly to be deprecated and should be prevented. =The Lesions and Secretions which Convey Infection.=--As far as acquired syphilis is concerned _absolute contact_ is necessary between the infecting material and the infected area, while upon the latter must exist some abrasion of the surface. Chancres and the early eruptions or mixed lesions have been proved to be absolutely virulent. The genitalia of both sexes are frequently the site of wart-like lesions referred to as condylomas, which are usually kept more or less moistened by the secretion of the parts, and are fruitful sources of contagion. _The discharging lesion of those suffering from syphilitic disease should be regarded as capable of transmitting it_, while during the primary and secondary stages the blood and lymph should be regarded as probable sources of danger. Inoculation with the blood of patients during these stages has been known to be successful. How long the blood retains its power of infection is uncertain; it is usually regarded as free from it when the disease is latent. The _natural and physiological secretions of various organs_, _e. g._, saliva, milk, perspiration, tears, and urine, are not generally believed to _be capable of transmitting the disease_. The semen of syphilitic men may reproduce the disease by heredity but not by direct inoculation. It is possible under these circumstances for the father to transmit the disease to the ovum without previously infecting the mother; such infection of the ovum by diseased spermatozoa is quite different from the infection of the ovum by the mother who has acquired the disease, the father having escaped it.