July 15, 1897] 



NATURE 



249 



THE ETIOLOGY OF YELLOW FEVER. 



YELLOW fever is an acute infectious disease, 

 endemic in the West Indies, the shores of the 

 Mexican Gulf, and in some parts on the West Coast of 

 Africa, whence the disease has been repeatedly trans- 

 ported into other localities, causing here epidemic out- 

 breaks. Like other infectious diseases, yellow fever is 

 supposed to be caused by a specific living entity which, 

 invading a predisposed person, multiplies there and 

 causes the peculiar pathological changes in the gastro- 

 intestinal tract and the liver, characterising yellow fever. 

 Within recent years the supposed specific microbe has 

 been discovered several times. Dr. Domingos Freire, 

 of Brazil, and Dr. Carmona y Valle, of Mexico, have 

 announced such discovery, but Dr. Sternberg, of Wash- 

 ington, who has himself studied the disease on behalf of 

 the United States Government, has shown that none of 

 these discoveries are a reality, and after a prolonged 

 investigation, including the examination of a great many 

 cases afiected with, or dead from the disease, has arrived 

 at the following ccnclusions, embodied in a lengthy 

 report to his Government : that none of the different 

 species of bacilli' and cocci, present in the intestinal 

 canal, in the blood, the liver and other tissues of persons 

 affected with yellow fever, can have a claim to be con- 

 sidered as the specific microbe ; that in a number of 

 cases the examination, microscopic and cultural, of the 

 blood and tissues yielded no bacteria recognisable either 

 by the known methods of staining or culture ; and he 

 finally implied that the specific microbe of yellow fever 

 is most probably not of the nature of a bacterium at all. 

 After these very definite conclusions by Dr. Sternberg, 

 it came rather as a surprise when, some months ago, the 

 announcement was made that Dr. Sanarelli, Professor of 

 Experimental Hygiene in Montevideo, formerly in the 

 Pasteur Institute in Paris, had discovered the true cause 

 of yellow fever in the form of a bacillus, Bacillus 

 ictcroides. This surprise is still further heightened by 

 the statement in Dr. Sanarelli's lecture, that the Bacillus 

 icteroides is demonstrable by the ordinary methods of 

 staining and by culture in the ordinary well-known 

 media. The morphological and cultural characters of 

 the bacillus show it to belong to the group of coli-like 

 bacilli ; it is rarely demonstrable in a pure state in the 

 blood or tissues, being generally associated with a more 

 or less copious admixture of other microbes — Bacillus 

 coli coiinnunis, streptococci and stap/iylococci ; as a rule it 

 is present only in small numbers in the capillary blood- 

 vesiels of the liver, spleen and kidney. It reflects great 

 credit on the perseverance and sagacity of Dr. Sanarelli 

 to have been able, notwithstanding all these difficulties, 

 to select out the Bacillus icteroides, and to have by animal 

 experiment been able to demonstrate, at least, as highly 

 probable that the Bacillus icteroides is the true microbe 

 of yellow fever. As mentioned just now, the distribution 

 of the microbe in the affected person, its morphological 

 and cultural characters do not in themselves offer strong 

 prima facie evidence, and Dr. Sanarelli himself fully 

 recognises this ; but when we come to the experimental 

 evidence which he furnishes, the evidence as to the 

 Bacillus icteroides being the specific cause of yellow fever 

 assumes considerable power. 



In the first place, Sanarelli shows that dogs, goats, and 

 horses are susceptible to infection both with the living 

 bacilli as also and particularly with the highly poisonous 

 toxin produced by the bacilli in broth culture ; the 

 symptoms and anatomical lesions hereby produced in 

 these animals in the intestinal tract, the liver and the 

 kidney, bear a striking resemblance to those of yellow 

 fever in man. In the second place, Sanarelli furnishes 

 proof that the toxin produced in broth culture — and 

 separated from the bacijlary growth by filtration through 

 a Chamberland filter — when injected into healthy persons 



NO, 1446. VOL. 56] 



causes a prompt reaction in the form of severe dis- 

 turbance, primarily of the intestinal tract, but also, 

 further, of the general system closely resembling that in 

 yellow fever. It is to be hoped, nay, it inay be assumed as 

 certain, that in continuing his investigations Dr. Sanarelli 

 will ascertain the action of the blood of human beings, 

 who have passed through, and recovered from the disease, 

 on the Bacillus icteroides. This disease, as is well 

 known, very rarely occurs twice in the same person, and 

 it is therefore highly probable that, as is the case in 

 other similar infectious diseases, the blood after a single 

 attack possesses agglutinating action {in vitro), or germi- 

 cidal action {in corpore), or both on the culture of the 

 specific microbe. If on further investigation the blood 

 serum, after an attack of yellow fever, should be found 

 to show such positive actions on the Bacillus icteroides, 

 a strong support will thereby be furnished as to this 

 bacillus being the specific microbe. It will be the 

 crowning of prolonged and laborious studies, if Sanarelli 

 by experiments on immunisation of animals — the horse 

 being evidently well fitted for such immunisation — did, 

 as is highly probable that he will, obtain antitoxic serum 

 by which yellow fever can be successfully combated both 

 prophylactically and therapeutically. E. Klein. 



THE VARIABLE STAR i? AQUIL.E.' 



THIS essay contains a full discussion of all the 

 available observations of a remarkable variable 

 star, the fluctuation of whose light presents many 

 features the explanation of which is still beset with 

 much difficulty. Of the 12,000 recorded comparisons of 

 the relative brightness of j; Aquilie and neighbouring 

 stars, no less than 7147 are due to the indefatigable 

 perseverance of Julius Schmidt, who for the last twenty 

 years of his life (1859- 1879) was director of the observ- 

 atory at Athens. Taking advantage of the preponder- 

 ance of Schmidt's records over those of all other 

 observers, the author first investigated the variations of 

 the star's light as shown by these alone, and then 

 examined in how far the results thus obtained were 

 confirmed by the labours of other observers. The dis- 

 cussion of Schmidt's observations was complicated by 

 the circumstance that in the majority of cases he only 

 used two comparison stars, i3 and i Aquilai, one of which 

 there was great reason to believe was itself variable. 

 From the 1700 occasions on which both stars were used, 

 Dr. Lockyer found t to vary 17 grades of Schmidt's 

 scale with a period of about thirty-five years. Associated 

 with this long-period change, the relative brightness of t 

 was shown to be subject to an annual variability of about 

 one grade, which is clearly traced to the influence of the 

 hour angle at which the stars were compared. This 

 apparent annual variation is, therefore, identical with 

 the "position error" noted by many observers of 

 variable stars, and which has lately been investigated 

 so thoroughly by Mr. Roberts, of Lovedale, South 

 Africa. Schmidt's observations, freed from both the 

 above variations as well as from the slight aberration 

 error due to the changing position of the earth in its 

 orbit, were all reduced to the meridian of Bonn. Owing 

 to the general sparseness of the data, it was necessary 

 to combine the observations of 100 periods, or about two 

 years, into a group represented by a single curve. This 

 was effected with the help of a provisional mean period 

 and date of minimum for which Argelander's values of 

 7d. 4-234444h. and 1848, May i8d. 6-4333h. M.T. at Bonn 

 were adopted, the date being that of epoch 400. To 

 further facilitate the construction of the curve the mean 



1 " Resultate aus deii Beobachtungen des Veranderlichen Sternes 

 rt Aquila." Inaugural Dissertation zur Eriangung der Doctorwiirde, von 

 William J. S. Lockyer. 5 plates, quarto, pp. 95. (GOttmgen : 1897- 

 London : Dulau and Co.) 



