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SCIENCE 



[N. S. Vol. LII. No. 1357 



markable progress of events in connection 

 with a class of special microorganisms or 

 spirochetae, so called since Schaudinn's dis- 

 covery in 1905 of the pallida, the microbic in- 

 citer of syphilis. The search for the microbe 

 of syphilis had been unremitting since the 

 early days of bacteriology, and not a few false 

 claimants held the field for a brief space. 

 Schaudinn's discovery was very soon con- 

 firmed, and has now been firmly established; 

 and it is interesting to note that in fact it 

 was itself a confirmation of an observation 

 made a few years earlier by MetchnikofE and 

 Bordet, who, however, because of the tech- 

 nical difficulties of the quest did not succeed 

 in confirming their own findings. The un- 

 usual difficulties surrounding the detection of 

 the living pallida in the body fluids, because 

 of its extreme tenuity merely heighten the 

 respect we must hold for the zoologist 

 Schaudinn's perspicacity. Very soon stain- 

 ing methods were introduced to lighten the 

 task of detecting the pallida, but so capri- 

 ciously did they act and so baffling did the 

 ordinary microscopic detection prove, that the 

 great promise of the employment of the pal- 

 lida for purposes of diagnosis and treatment 

 was not at once realized. 



None the less, a great advance in bacteri- 

 ology had been achieved, and a new class of 

 microbes potentially disease-producing was 

 presented for study. Within a year a second 

 spirochete, called pertenuis, was discovered 

 in the lesions of yaws, a tropical disease hav- 

 ing certain affinities with syphilis. The search 

 for the delicate spiral organisms was not an 

 easy one, and only the masters of bacterio- 

 logical technique were likely to succeed in it. 

 Then suddenly the labor was lightened and 

 the road made smooth for a rapidly succeed- 

 ing succession of discoveries in this field by 

 the invention and application of the dark-field 

 or ultramicroscope. This instrument was per- 

 fected for observing dispersed particles in 

 colloidal solutions and, as many of you are 

 aware, operates by projecting powerful rays 

 of light in directions parallel to the surface 

 of the microscopic slide. Such a field if 

 optically empty will be dark and not lumi- 



nous; but if particles are present in it, the 

 rays of light will be intercepted and the par- 

 ticles illuminated. They in turn, and accord- 

 ing to their size, will appear as bright objects, 

 or when very small, give a diffuse luminosity 

 to the field. The phenomenon is similar to 

 the one described by Tyndall, in which a beam 

 of light passed through a dark space contain- 

 ing suspended particles causes them to become 

 visible. When the suspended matter consists 

 not only of dispersed particles, but of micro- 

 organisms, these also become luminous, and 

 when, as with the spirochete, they exhibit a 

 wavy structure and independent motion, they 

 at once arrest attention. To-day the dark- 

 field microscope is found in every well- 

 equipped clinic, and it has aided in adding 

 many new species to the already considerable 

 number of microbes known to be disease-pro- 

 ducing. 



The latest significant addition to this field 

 is the Leptospira icteroides, or the jaimdice- 

 producing spiral, which Ifoguchi has recently 

 detected in the blood and internal organs of 

 cases of yellow fever. His extensive investi- 

 gations carried on in Ecuador, Mexico, and 

 Peru, as well as at the Eockefeller Institute, 

 have rendered it highly probable that this 

 spirochete is the microbic incitant of that 

 severe epidemic disease. 



Tellow fever, as you know, is an insect- 

 borne disease and arises from the insertion 

 into the blood of man of a virus carried by 

 a particular mosquito — Stegomyia calopus. 

 After the mosquito transporting the virus has 

 bitten a healthy person, an interval of about 

 five days elapses before his blood becomes in- 

 fective, and the infectiousness endures about 

 three days longer. During the latter period 

 the blood seinmi can be passed through the 

 finest-grained porcelain filters without losing 

 its infectivity. On the other hand, a normal 

 mosquito which has bitten a yellow fever 

 patient, does not become capable of infecting 

 other human beings until after about twelve 

 days. Hence the insect acts not merely pas- 

 sively, as a needle might, as the conveyer of 

 the virus, but is necessary in order to increase 



