Pathogenesis and Specificity 725 



centrifugated for a short time to throw down scraps of the nutrient 

 tissue, the fluid then decanted and recentrifugated rapidly and for 

 a longer time to throw down the micro-organisms. 



Pathogenesis and Specificity. — There can be no doubt about the 

 causal relation of Treponema pallidum to syphilis. It is unknown 

 in every other relation; it has appeared in every required relation, 

 and thus has completely fulfilled the laws of specificity laid down by 

 Koch. Treponema pallidum is not only pathogenic for man, but, 

 as has already been shown, can also be succcL^sfuUy implanted into 

 chimpanzees, macaques, rabbits, guinea-pigs, and other experi- 

 ment animals. As syphilis is, however, unknown under natural 

 conditions, except in man, it may be looked upon as a human 

 disease. 



The organism enters the body through a local breach of con- 

 tinuity of the superficial tissues, except in experimental and con- 

 genital infections, where it may immediately reach the blood. 



In ordinary acquired syphilis the point of entrance shows the 

 first manifestations of the disease after a period of primary incuba- 

 tion about three weeks long, in what is known as the primary lesion 

 or chancre. This appears as a papule, grows larger, undergoes super- 

 ficial indolent ulceration, and eventually heals with the formation 

 of an indurated cicatrix. It is in this lesion that the treponema 

 first makes its appearance. From this lesion, where it multiplies 

 slowly, it enters the lymphatics and soon reaches the lymph-nodes, 

 which swell one by one as its invasion progresses. During this 

 stage of glandular enlargement the organisms can be found in small 

 numbers in juice secured from a puncture made in the gland with 

 a hollow needle. This period of primary symptoms (chancre and 

 adenitis) includes part of what is known as the period of secondary 

 incubation, which intervenes between the appearance of the chancre 

 and that of the secondary symptoms. It usually lasts about six 

 weeks. During this time the organisms are multiplying in the 

 lymph-nodes and occasionally entering the blood. What fate 

 the organisms meet when they reach the blood in small numbers is 

 not yet known, but the slow invasion suggests that those first enter- 

 ing are destroyed, and that it is only when their numbers are great 

 and their virulence increased that they suddenly become able to 

 overcome the defenses and permit the development of the secondary 

 symptoms. The period of secondary symptoms corresponds to 

 the invasion of the blood by the parasite. It may continue from 

 one to three years, during which time the patient suffers from 

 general symptoms, fever, etc., probably due to intoxication and 

 local symptoms, such as alopecia, exanthemata, etc., due to local 

 colonization of the organisms. At the end of this period a partial 

 immunity, such as is seen in other infectious diseases (malaria), 

 develops, the organisms disappear from the blood, the general local 

 and constitutional disturbances recover, and the patient may 



