134 



NATURE 



[June 6, 1895 



Cairo, both as regards days and seasons. Relative humidity 

 \-aries much more at Cairo than at Alexandria, but it is much 

 lower at Cairo in summer, and a little higher in winter than at 

 .Uexandria; while, on the contrar)', the absolute humidity varies 

 much more at Alexandria, being verj' high in summer and con- 

 siderably greater than at Cairo. Both places enjoy a lan;e 

 amount of sunshine, but fog occurs occasionally, more particu- 

 larly at Cairo in the early morning. 



\ MOST important contribution to the study of the formation 

 of dolomite is made by M. C. Klement, in the Bull. Soc. Bclgc 

 CM. Paliontol. el Hydrol. .\fter describing the history of 

 theories of dolomite, the author calls attention to the frequent 

 occurrence of dolomite in the form of coral-reefs, as obser\ed by 

 Dupont in the Devonian, by Richthofen and Mojsisovics in the 

 Trias, antl by Dana in the recent raised reefs of Metia in the 

 I'acific. He |K>ints out that while in the chemical experiments 

 that have Iwen made with a view of dolomitising carbonate of 

 lime, laltile has always been operated on, the substance of coral 

 has been show n by Sorby to he probably aragoiiite. The author 

 has therefore carried out a large series of experiments on the 

 action of the constituents of sea-water (particularly magnesium 

 sulphate) on aragonite, the results of which are given at full 

 length. From these he finds ( I ) that a solution of magnesium 

 sulphate, in the presence of sodium chloride, and at a tempera- 

 ture of 60' C. or more, decomposes aragonite with formation of 

 a magnesium carbonate the exact composition of which is difficult 

 to determine, owing to the impossibility of isolating it from the 

 rcsirlual aragonite : (2) that this action increases with the rise 

 of temperature., and with i\\e louceutratioii of the solution, and is 

 greatly diminished by the absence of sodium chloride : (3) that 

 recent coral is attacked by magnesium sulphate just as mineral 

 aragonite is ; and (4) that the lagoons of mmlern coral-reefs aflord 

 all the conditions of lemj>erature, saturation, Cv;c., necessary for 

 the prixluction of magnesium carbonate in the manner of his 

 exjxrriments. While recognising, therefore, that dolomites may 

 have l)cen formed in more ways than one, M. Klement concludes 

 that one of the most usual ways of formation of dolomite in 

 nature has Ijecn the action of heated and concentrated sea-water 

 in coral-lagoons on the aragonite of coral and other skeletons, 

 with formation of carbonate of magnesium, which is subsequently, 

 l)erha|)s after solidification of the rock, with the remaining car- 

 Imnate of calcium, converted into massive dolomite. 



The last numljer of Modern Mediiiue and Baeteriohgieat 

 A'ei'iew is of exceptional interest, inasmuch as it contains an 

 original article by I'rof. Melchnikoff, of the Pasteur Institute, on 

 "the extra-cellular destruction of bacteria in the organism." 

 This article is really a critical comment u|5on some of the 

 conclusions deduced by Dr. I'feiffer from his cxperimenLs on the 

 destruction of cholera vibrios in the peritoneal cavity of guinea- 

 pigs. Dr. I'feiffer obscr\cd this ficstruction of cholera vibrios 

 when the latter were introduced into animals previously 

 vaccinated against this germ, and also in the case of unprotected 

 animals when the vibrios were injected together with a small 

 <|uantity of scnmi from vaccinatc<l animals. In both cases Dr. 

 I'feiffer found that they were destroyed outside the cells in the 

 jicritoneal fluid, and he tjelieves that this bacteria-killing fluid is 

 secreted by the cellular elements in consequence of a special 

 excitation prmluccd by the injection of cholera vibrios, and 

 that the immunity acquired by guinea-pigs is independent of 

 phagocytosis. I'rof. Metchnikoff, however, regards this as an 

 epivxic in the liatlle between liacteria and phagocytes, and 

 maintains, on evidence sup|x)rted by experiments, that the 

 leucr)cytcs secrete this Inctcria-killing fluid whilst imdergoing 

 a process of degeneration due to the injection of I'feiffer's 

 mixture of vibrios, serum, and broth. That although unable 

 10 engulf the vibrios, they are able still to destroy them by their 



NO. 1336, VOL. 52] 



secretions. . Metchnikoff |x>ints out that if before introducing 

 the vibrio-mixture, a few cubic centimetres of broth be injected 

 into the peritoneal cavity, the leucocytes will gather together in 

 great force after a few hours, and if the vibrio-mixture lie then 

 introduced, phagocytosis does take place, and the cholera 

 bacteria are more rapidly destroyed by this process of intra- 

 phagocytosis than by the extra-cellular destruction produced by 

 the conditions of I'feiffer's experiments. The mechanism of 

 immunity is surrounded with so many complicated i>roblems 

 that the search for its solution, whilst one of the most interesting 

 tasks afforded by the developments of bacteriology, must still 

 remain one of the most puzzling and ditiicvilt. 



Thk current number of \\\e Journal de Physique contains an 

 important (mper by M. P. Curie on the magnetic properties of 

 bodies at different temperatures. The author has examined the 

 magnetic properties of a number of substances in fields of from 

 25 to 1350 C.G.S. units, and in simie cases for temperatures 

 from 1 5° to 1 370° C. The body un<ler observation was generally 

 in the form of a coarse powder, and was enclosed in a glass bulb, 

 which was |)laced in a non-uniform magnetic field produced by 

 two electro-magnets. The force acting on the body was 

 measured by means of the torsion of a wire. For the purposes 

 of heating the glass bulb was surrounded by a fine clay jacket, 

 and this latter was heated by a wire in which an electric current 

 was passe<l, the temperature being measured by means of a 

 thermo-electric junction. In the case of diamagnetic bodies, w ith 

 the exception of bismuth and antimony, the author finds that 

 temperature has practically no effect on their magnetic pro- 

 perties. Fusion and allolropic modification also seem to pro- 

 duce no effect, so that the magnetic properties of a body seem 

 ' to dei>end not on the arrangement, but rather on the 

 nature of the molecules of the body. Selenium, however, is 

 an exception, for in this case the susceptibility is about 3 or 4 

 ]ier cent, smaller in absolute value in the liquid than in the solid 

 state. Phosphorus is another exception, for the susceptibility 

 of the different allotropic modifications are slightly different. 

 The susceptibility of bismuth increases with rise of temperature, 

 according to a straight line law, uji to the melting-point, where 

 there is a sudden rise. The susceptibility of melted bismuth is 

 independent of temperature, and is very nearly o. Observations 

 made on oxygen show that the cocfticient (K), which, when 

 multiplied into the strength of the magnetic field, gives the 

 magnetic moment of the body per unit mass (the author calls 

 this the coefficient of specific magnetisation), is imle|)endent nf 

 the pressure, .and is between 20' and 450° inversely proportional 

 to the absolute temperature. In the cise of solutions of para- 

 magnetic salts, K is also found to vary inversely as the absolute 

 temi>erature ; thus supporting the observations of Wiedemann and 

 PIcssner im this subject, (ilass when cold is generally feebly dia- 

 magnetic ; when heated, however, it becomes nuich more strongly 

 diamagnetic. The rate of incre.aseof the dianiagnetism decreases 

 as the lemiK-rature rises ; above 300° C. no further change takes 

 place. The author considers these changes to be tlue to the 

 fact that glass consists chiefly of a diamagnetic substance, the 

 pro|K'rties of which remain ima1lere<l when the temperature 

 rises, and of a small quantity of a relatively strimgly para- 

 magnetic substance, the para-magnelism of wiiich liecreases as 

 the temperature rises. 



.\Ikssrs. GEORtiK I'liil II' wii Son will shortly publish "The 

 Kxploralion of Australia," by Mr. -Mberl F. Calvert. This 

 book is designed to form a companion volume to Mr, Calvert's 

 work, "The Discovery of .\ustralia," and will trace the 

 progress of maritime and land exploratitm frem the period of 

 Captain Cook, up to recent times. 



.\ IRANSIAIION, by Mr. W. K. Haxter, i , anniiunce<l of \au 

 Hcurck's im|>ortant treatise on the Diatomacea-. Il will 1 .miaiu 



