June ii, 1903 j 



NATURE 



127 



^(.pliy from the time of Plato has had its own way of meet- 



ini,r it on its own ground, and disposing of its exclusive 



(laims. I do not write here in the interests of trans- 



( .ndentalism, but merely to invite the attention of 



jihvsicists to a point of view which students of modern 



;.-vchology have borrowed from it, and are now generally 



king to apply to the problem of the relation between 



ntal and physical energy. J. H. Muirhead. 



liirmingham, June 9. 



Seismometry and Geite. 

 Had Dr. Chree (Nature, May 21, p. 55) referred to the 

 various papers about earthquakes in the reports of the 

 ''ritish Association commencing in 1847 by William 

 pkins, in the now somewhat antiquated Transactions 

 the Seismological Society of Japan, and in very many 

 ocner publications relating to earthquakes, he would have 

 seen that his instructive remarks relating to the propaga- 

 tion of waves in an isotropic medium were but repetitions 

 information with which seismologists have at least a 

 :_;ht acquaintance, whilst the suggestion that the velocities 

 -uch waves have been regarded as having a direct con- 

 [ •ition with Young's modulus is incorrect. 



In connection with Bessemer steel. Young's modulus 

 was mentioned, but I do not see that it was referred to 

 repeatedly (Nature, April 9, p. 538). In 1897 Dr. Chree 

 made an attempt to calculate Young's modulus and the 

 bulk modulus for the earth, but the grist he used was so 

 doubtful in character that his results are not convincing. 

 From some source or other he discovered that wave veloci- 

 ties of 125 and 25 km. per second had been determined, 

 and these were assumed to be \\ and \\ for compressional 

 and distortional waves passing through the world. One, 

 if not both of these, are based upon arcual measurements ; 

 they are incorrect at that, and the latter seems more likely 

 to represent the velocity of a surface undulation rather 

 than a quantity corresponding to \\. 



What I pointed out was that recent determinations of 

 a quantity probably corresponding to V, find a simple 

 explanation by the assumption of a core that is fairly 

 homogeneous and of fairly definite dimensions, which is 

 not the solution of the seismological problems attempted 

 by Dr. Chree. The reference to elastic moduli was in- 

 cidental. 



The chief objection raised to the iron core is not that 

 iron, as we know it, will not convey vibrations at the 

 observed speeds, but that if we take such a core, gravita- 

 tional and astronomical requirements appear to be such that 

 !it must have dimensions which do not altogether accord 

 with the interpretation given to seismometrical observations. 

 What Dr. Chree tells us about the possible relationship 

 between seismic disturbances and the movements of mag- 

 netic needles is as well known to seismologists as what he 

 has to say about wave velocities. Many of the chief mag- 

 netic observatories of the world have compared their 

 magnetograms with long lists of world-shaking and other 

 earthquakes, and the results are to be found in the British 

 Association Reports, 1888 and 1889. From Dr. Chree's 

 own comparisons at Kew (British Association Report, 1888, 

 pp. 229 and 231, &c.), the movements he discovered were, 

 ' with two possible exreptions, of " the ordinary magnetic 

 I small wave type," which " go on for hours if not for days." 

 My conclusion is that at Kew, Greenwich, &c., needles 

 seem not to be disturbed at the time of large earthquakes 

 in the manner in which they are disturbed at Bombay and 

 other places. At these latter places, where the movement 

 of needles apparently accompanying the passage of the 

 large waves indicates a possible magnetic disturbance 

 directly due to seismic causes, the inference I made was 

 ! that at such places H.F. and (g — y) may be abnormal. 

 I As an illustration of the coexistence of the three pheno- 

 I mena we may take the following : — 



H.F.(c.g.s.) 



Kew 0-18451 (1901) 



Bitavia 0-36752 (1898) 



Earthquake 

 (.t> — y/cm. effect on 



magnetic needlps 

 + 40 (igoo) Undisturbed. 

 + 136(1894) Disturbed. 



T 



Whether these coincidences are accidental or general, 

 ' liservations are yet required. John Milne. 



NO. 1754, VOL (38] 



THE VITALITY OF THE TYPHOID BACILLUS."- 

 HE object of hygiene is to prevent disease. It is 

 therefore necessary that the factors in the causa- 

 tion and dissemination of disease should be understood 

 in order that adequate preventive measures may be 

 adopted. The living agents responsible for the pro- 

 duction of infectious diseases when they are dis- 

 charged from affected individuals may find their way 

 bacli to the human body by a number of indirect 

 channels. The water, the soil, or the food may at 

 times harbour and transmit the germs of disease. The 

 conditions under which these morbid agents exist in 

 the outside world constitute one of the most important 

 subjects of hygienic inquiry. It cannot be said with 

 regard to this phase in the life-history of pathogenic 

 organisms that our knowledge is as accurate or ex- 

 tensive as it is in other directions. This is due to 

 the difficulties that stand in the way of such investiga- 

 tions. The germs of disease undergo an enormous 

 dilution in the air, water and soil, whilst they tend 

 to become lost in the crowd of similar forms already- 

 existing in nature. The facts so far support the view 

 that the parasitic microorganisms possess a consider- 

 able amount of resistance to external influences, and 

 that the links which ensure their conservation and re- 

 transference to man are numerous and varied. A 

 typical example is the bacillus of typhoid fever. This 

 organism may become widely distributed through the 

 dejecta. It may contaminate a water supply and 

 directly, or by the agency of milk, produce a fresh 

 outbreak of typhoid fever. It may infect the soil, and 

 through it a number of raw vegetable foods. Its pre- 

 sence has been detected in the sewage-fed oyster, 

 whilst tainted dust and flies aid in the distribution of 

 the organism. 



In studying the distribution of enteric fever, a phys- 

 ical factor which has to be considered is the influence 

 of cold on the vitality of the specific organism. The 

 effect of low temperatures upon microorganisms 

 generally has formed a subject of inquiry from time to 

 time. The latest experimental work has conclusively 

 shown that bacteria retain their vitality under the 

 most adverse conditions of cold that it is possible to 

 devise. Prof. Sedgwick and Mr. Winslow, approach- 

 ing the subject from the hygienic point of view, have 

 carefully studied the influence of natural and normal 

 conditions of cold upon the typhoid bacillus in par- 

 ticular. Their experiments were carried out with 

 special reference to the danger of conveyance of the 

 disease in question by polluted ice, and with reference 

 to the seasonal distribution of the disease. The matter 

 was undoubtedly one that called for investigation, and 

 notably in a country where ice and iced drinks are in 

 such universal demand. The authors were unable to 

 find any recorded evidence of a conclusive character as 

 to the spread of typhoid fever by a polluted ice supply,, 

 although it has been a common opinion that ice might 

 be an important source of infection for typhoid fever 

 and other intestinal diseases. 



The apparent purity of ice is deceptive. It is true 

 that water in freezing undergoes a certain amount of 

 purification. It loses, on conversion into ice, saline 

 constituents, contained air, and a certain proportion of 

 organic suspended matter. At the same time, it is 

 not entirely freed from microbes. The figures quoted by 

 Prof. Sedgwick and Mr. Winslow show that snow-ice 

 may contain an a\(>rage of more than 600 bacteria per 

 cub. cm. lii^Lir. V are also given to indicate the enor- 



1 Experiments on the Effect of Freezing and other Low Temperatures, 

 upon the Viahility of the Bacillus of Typhoid Fever, with Considerations 

 regarding Ice as a Vehicle of Infectious Disease " By William T. Sedgwick, 

 Ph.D., Professor of Biology, and Charles-Edward A. Winslow, b.M. 

 Instructor in Biology in the Massachusetts Institute of Technology 

 (Memoirs of the American Academy of Arts and Sciences, vol. xii. No. 5, 

 1902.) 



