Arr.rsT, 1901.] 



KNOWLEDGE. 



189 



The fact that during tlie progress of a disease the 

 blood acquires properties iniinieal to tlie gi-o\vtli of the 

 bacteria is very marked in the case of typhoid, and 

 affords a means of diagnosing the disease. If we examine 

 microscopically a drop of broth containing a young 

 culture of the typhoid bacillus, we see the deadly plants 

 darting and wriggling about the field in all directions. 

 On diluting the drop with healthy blood-serum, no loss 

 of activity is to be seen, but if the added serum is that 

 of a patient suffering from typhoid, the movements slow 

 down, and the bacilli seem as if paralysed. They collect 

 in separate clumps, strongly suggesting different swarms 

 of midges, and in a minute or two all is over. The 

 bacteria are dead. The sight is, in its way. as striking 

 as anything I have seen. It irresistibly brings up before 

 the imagination the fierce struggle which goes on when 

 disease-germs invade the body. Should they escape 

 arrest by the '' policemau-cells,' they begin their deadly 

 work, but all the reserve forces of the invaded country 

 are called out. The intruders have first to fight against 

 the healthy fluids of the body. If the.se are unsuccessful 

 the bacteria live and niultipjy and give off their poisons. 

 Immediately, however, the body responds and brings 

 forward a supply of antitoxins. Then it is war to the 

 knife. If the bacteria can produce toxins faster than 

 the body can supply antitoxins, they win, and the 

 patient sinks. The only hope is that, before general 

 collapse has gone too far, a timelv injection of the 

 required antitoxin maj^ put the enemy to rout. 



The possibility of the last resource is due to the 

 labours of such men as Pasteur, Lister, Koch, and their 

 followers. They have shown that we have to fight for 

 our lives against enemies, unimaginably small, but 

 present everywhere and in countless mjTiad&; but they 

 have also been able to classify the foes into races and 

 nations, to discover their various methods of attack, and 

 in many cases to forge weapons by which these attacks 

 may be foiled. The work is only in its infancy, but 

 there is every reason to believe that its ultimate achieve- 

 ments will do more for the well-being of mankind than 

 any other nineteenth-century discovery. 



Conducted by >r. I.Cro§s 



Microscopic Tisiox.^A paper of unnsual interest entitled 

 " An examination of the Abbe Diffraction Theory of the 

 Microscope,'' was submitted for the consideration of the Royal 

 Microscopical Society by ^Ir. J. W. Gordon, at the meeting 

 held on June 19th last. It was sought to demonstrate that 

 many of the experiments on which the Abbe theory is based 

 were fallacious and incorrectly interpreted, and new ideas con- 

 cerning the formation of the microscopic image were given. 



It would be impossible, in the space at my disposal, to give 

 even a brief rei^urne oi the paper, for it will occu])y probably 

 tifty pages of the Society's journal, added to which I have not 

 an advance copy of it before me, and only had an opportunity 

 of examining it for a short time during the few days it was at 

 my disposal. To do it justice, it will require to be read with 

 consideration, and the experiments described actually worked 

 out. 



A paper of this description is of immense value, because it 

 brings prominently before present-day microscopists straight- 

 forward statements which each can for himself verify or 

 disjirove, and, by comparing them with Abbe's exiieriments. 

 gain considerable information on this interesting subject. The 

 matter will surely give rise to discussion, and it is to bo hoped 

 that a tangible result may follow. 



So far as the Abbe theory is concerned, it has to bo borne in 

 mind that Abbe's original pajjors were written more especially 

 for those who had the bonetit of a (lernian LTniversity training 

 in phj'sics, and the actual experiments which Mr. Oordon in his 

 paper seeks to disprove in some degree were intended, not as a 

 com])lete proi^ ol his theory, b\it as ocular demonstrations of 

 some of his statements such as would appeal to those who had 

 not had such traimng. 



It has to be remembered further that the whole of Abbe's 

 experiments are based on the assumption that the light used is 

 parallel from a di.stant source, and directly the illuniinant is 

 brought near, as is the case in ordinary microscopical work 

 where a lamp or a sub-stage condenser is used in focus, the 

 whole circumstances .are changed and the experiments cease to 

 convince. 



The jiublication of the paper will be awaited with interest, 

 for it has awakened a doubt in some minds as to whether the 

 microscopic;d imago that is really utilized is intlucnced more by 

 effects behind the objective produced by its aperture, than by 

 diffraction effects in the object under examination. Under 

 modern conditions of working where a condenser yielding a 

 large .aplanatic cone is used the condition of a self luminous 

 object is practically reali.sed, for in such a case each point of 

 the flame reaches one conjugate ])oint in the flame image, and 

 if that flame image is brought into correspondence with the 

 object, each part of the lamp flame lights one point of the 

 object. AD the points are separately illuminated and are 

 therefore not ca])able of interference in a very marked degree 

 (although as a matter of fact there is slight interference), hence 

 the value of our modern wide aplanatic cones of illumination. 



PRi;si:uvrN(; .and Mountin'i; Mosv''rroEs. — Some time has 

 elapsed since the connection between mosquitoes and malarial 

 fever was established, yet satisfactory sjieeimens of the former 

 have reached England in very small numbers although medical 

 men and others who are interested in the matter have constantly 

 wished to obtain them. 



The reasons are that the unmounted specimens are npt put 

 up in suitable preservative medium for travelling, or if they 

 are mounted, sufficient care has not been exercised in the 

 process. Several methods have been pubhshed in medical 

 papers on the subject of preserving mosquitoes, but none of 

 them are really satisfactory ones. The following will be found 

 to answer the purpose : — 



To send unmounted mosquitoes by post they should be 

 preserved in dilute alcohol, two parts of rectified spirit to one 

 part of water. Too many should not be put into one bottle or 

 they become entangled and broken. 



To make permanent mounts, dilute glycerine, .say one part 

 glycerine to two parts water, in a shallow cell will be found 

 best. The following is the process : — 



(1) Remove the dilute alcohol and soak in water until all 

 trace of the spirit is removed. 



(2) Soak in dilute glycerine for about twelve hours. 



(3) 3Iake cell, and when dry fill up with dilute glycerine and 

 carefully place the specimens in it and apply the cover glass. 

 Should the mosquito be too opaque after soaking in water, 

 place it in a strong solution of carbolic acid for a few hours, and 

 when transparent wash in water, then place in dilute glycerine. 



Portable Microscopes. — At this season cf the year when so 

 many microscopists are travelling in search of health and 

 pleasure, attention may be directed to a note on this subject in 

 the April number of the Jotimnl of the Queheti Mii-roacopical 

 CI III,. 



It has often been remarked that effects can be obtained with 

 large microscopes which cannot be secured with those of smaller 

 size, and the home-worker invariably chooses a model of such 

 large proportions as to render it unfit and inconvenient for 

 carrying on short trips and holidays. 



The provision of a companion microscope of .small size but 

 yet of a thoroughly .serviceable character becomes very desirable. 



