58o 



KNOWLEDGE & SCIENTIFIC NEWS. 



[November, 4906. 



Sydney by Ashhurton Thompson (1902, 1903, 1904); in 

 Port I-;iizalicth by Blackmore (1902); in Hons^ Kong by 

 Hunter (1904): as well as in Cape Colony by Mitchell 

 (1906); in Queensland by Baxter-Tyrie (1905I; and for 

 Calcutta by Pcarsc (1905). In India the connection was 

 scientifically indicated, if not established, bv .Snow and 

 AVeir (iSijj-), llawkin (1898), and the German com- 

 mission (1899). But as late as the report of the last 

 Indian Plague Commission (1903) no definite conclu- 

 sion was reached as to the share which rats take in 

 disseminatino- plague. (The introductory preface in 

 commenting on the contradictory nature of the evi- 

 dence, remarked that it was not clear whether rats 

 contracted the disease after its appearance among .the 

 human community, or whether they introduced it, or 

 even whether it was shared by human being and rat 

 alike.) 



There have been similar difficulties in determining 

 how the infection was conveyed from rats to human 

 beings, or from rats to rats. One way of conveying 

 the infection would arise from the cannibal practice 

 which rats betray of eating one another's dead car- 

 casses. But it has been shown that a very large amount 

 of plague-infected carcass absorbed in this way is 

 necessary in order to contract plague, and in any case 

 man would not contract the disease in this way. That 

 insects were the carriers of infection occurred to several 

 investigators. Yersin (1894), Hawkin (1897), Nuttall 

 (1897), Ogata (1897), and Simond (189S) examined flies, 

 ants, fleas, and bugs, and found plague bacilli in their 

 bodies, but though Simond succeeded in conveying 

 plague from rat to rat by means of fleas, there were a 

 number of unsuccessful experiments, and this want of 

 success was recorded by Nuttall and Tidswell, and by 

 the German Plague Commission, and by others who 

 believed in this method of transmission. A few 

 theorists objected to the hypothesis on other grounds; 

 the chief of which was that the rat-flea was indigenous 

 to the rat, and would not bite human beings or other 

 animals. These objections have been finally disposed of 

 by the identification of the characteristic rat-flea as 

 " Pulcx cheopis," and bv the proof that it will, and 

 does, bite other animals. 



We shall make the process of proof most clear by 

 recording briefly the results of the experiments made 

 bv the Plague Commission, (i) It was first shown by 

 confining rats in separate wire boxes, so that they 

 could not come into physical contact, that plague could 

 none the less spread from a plague-infected rat to a 

 healthy rat. (2) It was shown that plague might be 

 conveyed to guinea pigs in the same way. (3) On the 

 other hand, close contact of plague-infected animals 

 with healthy animals did not give rise to an epidemic 

 (epizootic) among the healthy animals if fleas were ex- 

 cluded. Nor did plague-infected animals, if the same 

 principle of exclusion was observed, convey the disease 

 to the young they were suckling. (4) When, however, 

 fleas were admitted to the colony of animals the 

 epidemic, once started, spreads from animal to animal, 

 the rate of progress being in direct proportion to the 

 number of fleas present. (Special precautions elimin- 

 ated the possibility of air-borne infection in these ex- 

 periments.) 



That plague can be conveyed from animal to animal 

 bv means of the rat-flea was thus shown, together with 

 a presumption that this was the principal means of con- 

 vcvance. This presumption is strengthened by other 

 experiments. It is shown both directly and indirectly 

 that in a plague-infected house the infection may be 

 due to the presence therein of rat-flea.s, which are cap- 

 able of tr.-^nsmitting the disease to animals. The direct 



proof was obtained by allowing guinea pigs to run free 

 in plague houses which had been pr(\ icusly disinfected, 

 but in which there were still fleas — as was shown by 

 their subsequent discovery on the guinea pigs. The 

 guinea pigs contracted plague, and the fleas caught on 

 them were found capable of conveying plague to healthy 

 animals. When guinea pigs, placed in a plague house, 

 were isolated in gauze covered cages in such a wa)' 

 that fleas could not reach them, the guinea pigs did not 

 contract plague. If in a cage where they could be 

 reached by fleas, the guinea pigs died in several cases. 

 The microscopic examination of the fleas which the 

 guinea pigs attracted in plague houses revealed the pre- 

 sence of the plague bacillus in their intestines. 



One indirect testimony to the superior effectiveness of 

 the flea as a vehicle of plague was afforded by the ex- 

 periments made with regard to the infectivity of plague 

 localities on the floors and walls of plague houses — 

 irrespective of the presence of fleas. The plague 

 bacillus disappeared from floors and walls much more 

 quickly than had been thought probable. It remains 

 to record the possibility that other insects besides fleas 

 may convey the infection, and a suggestion (nctsd in 

 the preface to the report) that plague may be a disea.sc 

 of fleas. 



Alcohol as a Stimulus to Life. 



Ix the second number of Scioice Progress (John 

 Murray) the place of honour is given to an extremely 

 lucid and suggestive article by Mr. W. B. Hardy, 

 F.R.S., of Caius College, Cambridge, in which he 

 treats of " The Physical Basis of Life " from the point 

 of view of the structure of atoms. In the course of the 

 article he refers to the various experiments of Messrs. 

 Maupas, Calkin, and Woodworth in estimating and 

 prolonging the number of generations of the tiny organ- 

 ism ParamoRcium caudatum. Normally the vital impulse 

 of this organism dies out after the 170th generation, 

 but Woodworth succeeded in prolonging its existence 

 to the 86oth generation by supplying it with appropri- 

 ate stimulant. The stimulant tried on the Paramoecia 

 with most success was — alcohol! " It was added to 

 the water in which the animals lived, so that they were 

 always immersed in one part of spirit in 5,000 to 10,000 

 of water " — an experience resembling in a diluted form 

 that of the Duke of Clarence's adventure in a butt of 

 Malmsey. In the effect produced there was the touch 

 of Nature which makes the whole world kin. The 

 periods of depression were wiped out. The curve of 

 vitality no longer showed the ominous recurrent falls. 

 At the same time the rate of growth and division, that 

 is to say, the physiological activity, was increased by 

 as much as 30 per cent. Something of the same effect 

 was produced bv strychnine, but there was a remarkable 

 difference in the fundamental action of the two drugs, 

 for whereas the beneficial effect of alcohol endured after 

 the drug ceased to be administered, that of strychnine 

 did not. Alcohol exacted no " physiological usury," 

 in spite of the prodigiously increased rate of living. 

 It was beneficial in its after effects. Other articles of 

 importance in Science Progress are " Some World's 

 Weather Problems," by Dr. W. J. S. Lockver; the 

 " Origin of Gymnosperms," by Mr. Newell Arbcr, and 

 " The Igneous Rocks," by Dr. J. W. Evans. 



Messrs. F. Darton and Co., the well-known manufac- 

 turine: opticians and scientific instrument makers, were 

 awarded a Grand Prix and Diploma d'Honneur at the Milan 

 Exhibition for their manufactures. 



