December 28. 1893] 



NA TURE 



211 



returned and fell ill with influenza ; strict isolation was even 

 then successful in preventing its spread to the inmates. 



Dr. Caldwell Smith's evidence as to retiology is valuable and 

 interesting. "It is to the life history of Pfeiffer's bacillus that 

 we must direct our attention if we wish to understand the 

 seemingly strange vagaries of the disease. An individual is 

 infected by breathing at once the expired air from a person 

 suffering from the disease, and I believe this to be the only 

 method of infection." 



The concourse of people is favourable to the spread of influenza 

 in two ways, according to Dr. Parsons : firstly, by bringing the 

 affected and the healthy near together ; and secondly, by the 

 poison being present in a more concentrated form in confined 

 and vitiated air. 



Among the discussions which throw light on the character of 

 the disease, and bear upon the means of preveniion, the following 

 may be mentioned : on the degree of protection afforded to 

 individuals and to communities by previous attacks, on the 

 influence of occupation and of unsanitary conditions, on the 

 connection with pneumonia, on the period of infectiousness, on 

 the clinical features of the later epidemics, and on relapses. 



The researches of Dr. Klein, in respect to the eftect of inocula- 

 tion upon animals, gave results for the most part negative. 

 His affirmative results, however, were " in full agreement with 

 the results obtained by Pfeiffer and Kitasato. " The bacillus 

 was always abundantly present in the bronchial secretion of 

 patients suff"ering from influenza, diminishing in number as the 

 disease abated. 



" It is to be feared," wrote Dr. Parsons, " that the contagion 

 of influenza is still domiciled among us, and that a renewal of 

 its epidemic activity within the next few years is by no means 

 improbable." The expected revival is now only too apparent. 

 A certain proverb declares, with the rashness of its class, that 

 the man once bit is twice shy. In a literal sense, the saying 

 may contain a good deal of truth, but to nations, or aggregations 

 of individuals, it is quite inapplicable. The development of 

 common sense for common action against these evils has still to 

 take place. This country has now passed through three severe 

 epidemics of influenza within four years, each outbreak 

 drawing many sad maladies in its train, prostrating hundreds 

 of thousands of breadwinners, cutting short many illustrious 

 lives, and crippling many for years to come, and we are now 

 running into a fourth epidemic in London, without any great 

 organised attempt being made to counteract it. 



The provisional memorandum of the Local Government 

 Board, issued on January 23, 1892, impressed upon the public 

 the fact that in its epidemic form influenza is an eminently 

 infectious complaint, communicable in the ordinary personal 

 relations of individuals with each other, that separation 

 of the sick from the healthy should as far as practicable be 

 carried out, that rooms, &c. should be disinfected, and that 

 ventilation should receive special attention. 



It would be some defence against a serious recrudescence of 

 the pest if this memorandum, or an abstract of it, were 

 supplied to every householder on the first thre.'itenings of an 

 outbreak in any locality. In his article on prophylaxis, Dr. 

 Parsons remarks on the difficulties which would frustrate 

 any measures of notification and isolation on a large scale, but 

 suggests that notification, with fees for early cases only, might 

 be tried in certain districts, and that such a measure should be 

 adopted '• in the interval before another epidemic." So much 

 experience has been gained in distinguishing the symptoms of 

 influenza from those of other ailments, that the difficulty of 

 diagnosis cannot now be an insuperable bar to attempts at 

 prevention. It is well to remember that the pecuniary cost of 

 prevention cannot be compared with the loss to the country by 

 an epidemic, for this has been proved to amount to millions. 



Among places and means of infection which may cause 

 much mischief, but are not noticed in this volume, are bakers' 

 shops, in which the baker or attendant suff"ers from influenza or 

 severe cold ; booking offices, post offices, banks, &c. in which 

 the mouth and the ledger, &c, are in multiple communication ; 

 letters written and fastened by patients ; and, most of all, 

 railway carriages packed full and with windows closed, daily 

 conveying vast numbers of people to and from the city, 

 and containing perhaps the most organically polluted air which 

 can easily be found in a civilised country. 



The report closes with an interesting statement respecting 

 the immunity of animals, including monkeys, at the Zoological 

 Gardens. R. Russell. 



NO. I 261. VOL. 49] 



f 



ON A METHOD OF SEPARATING THE 

 MINERAL COMPONENTS OF A ROCK. 



TT is told of a famous German petrographer, that whenever 

 appealed to by a student in difficulties over a problematical 

 mineral in a rock-slice, his invariable advice was "Get it out." 

 It is hard dispassionately to reflect on the sufferings to which 

 this simple process of "getting it out " have given rise, AH 

 we petrographers have passed through the vale ! May we now 

 indulge the pious hope that the following simple apparatus 

 may bring some mitigation to the ordeal ? It will certainly 

 save a good deal of time and trouble when only small quantities 

 of a particular mineral are required ; enough, that is, for a blow- 

 pipe analysis, a flame test, and microscopical examination. 



A large test-tube (see Fig.), conveniently six inches in length 

 by three-quarters in diameter, is filled with heavy solution, 

 graded from specific gravity 3'3 to 2*5, so as to form after 

 standing a diffusion column, as already 

 described in Nature, vol. xliii. p. 404, 

 1891. It is not necessary to wait till the 

 change in density of the column is uniform 

 from top to bottom ; by introducing a 

 sufficient number of specific gravity indexes 

 the column is mapped out into a succession 

 of lengths, within the limits of each of 

 which the change of density is practically 

 uniform, certainly sufficiently so for 

 mineral determinations. 



A fragment of the rock to be examined, 

 about the size of a hazel-nut, is powdered 

 in the usual way, sifted and washed, dried 

 and then introduced into the diffusion 

 column. Separation of the constituent 

 minerals at once begins to take place, 

 and in the course of a few hours is com- 

 plete. Each species of mineral is then 

 floating in liquid of its own specific 

 gravity ; the next problem is to get it out. 

 A pipette as commonly used is not suffi- 

 cient, for as it is introduced grains of 

 minerals from other zones than that sought 

 for, adhere to its sides ; on removing 

 the finger, the sudden inrush of fluid 

 carries with it grains from surrounding 

 zones, and finally on drawing up the 

 pipette, fluids of zones lying above that 

 to which it has descended displace the 

 heavier fluid it already contains, carrying 

 with them suspended grains, and thus 

 bringing about the mixture which it is 

 our desire to prevent. 



With very little trouble these difficulties 

 may be completely overcome. To prevent 

 the sudden inrush of fluid the pipette, 

 which should be of small calibre (in my 

 experiments it measures i*5mm.), is fitted 

 with a piston {p). This may be very simply 

 made by winding a little unravelled cotton 

 thread round the end of a stem of Esparto 

 grass, such as is sold for cleaning tobacco- 

 pipes. The piston is pushed down to the 

 bottom of the pipette, which is then ready 

 for use. 



To extract grains from any zone the pipette 

 is slid down into the diff^usion column till 

 its lower end is just immersed in the 



zone ; a gentle shake given to it as it passes through the solution 

 will serve to detach adhering particles ; the piston is then 

 slowly raised, and the fluid with its floating mineral grains 

 quietly follows it, the other zones remaining undisturbed. To 

 prevent the fluid of higher zones entering the pipette as it is with- 

 drawn, it is necessary to plug its lower end ; no very tight closure 

 is necessary, since the piston, which now lies at the upper end 

 of the pipette, by excluding the air ensures the retention of the 

 contained column of fluid ; all that is needed is a stopper, which 

 will exclude solid particles. A very thin glass rod is rounded 

 off" at one end, which is then bent upwards into the form of a 

 crook (r). The crook is let down into the diffusion column 

 till its upward pointing lower end lies beneath the open ex- 

 tremity of the pipette, which it completely blocks up on being 



\J) 



A test-tube con- 

 taining a diffusion 

 column. The figures 

 at the side indicate 

 corresponding specific 

 gravities : t, pipette 

 fitted with a piston 

 / ; c, crook by which 

 the lower end of the 

 pipette may be 

 plugged. 



