84 



KNOWLEDGE. 



March, 1915. 



been unfortunate enough for the victims in\-olved. Pre- 

 ventive medicine has now become the most important 

 branch of medical research, and the results which have 

 been obtained more than justify any methods that have 

 been decided upon at the present juncture. The danger 

 from epidemic diseases may, and probably will, become 

 more pronounced as the summer approaches ; but there 

 is this to be said : the longer it is deferred, the more efficient 

 become the means to combat the danger when it arrives. 

 One important factor — the water supply — has been dealt 

 with very thoroughly, and it is not too much to say that at 

 the present time arrangements are in force which, if only 

 carried out thoroughly, as they should be, leave little room 

 for any danger occurring either to the men under training, 

 or to those actually on service at the front. As to the 

 danger of wound infection, that is a very real one. Those 

 fighting in France are under the influence of a soil that is 

 highly manured, and which is as a result highly productive. 

 Its verjf productivity shows that it is a good bacterial 

 culture medium, and the result is that a wound, when it 

 occurs, is at once exposed to a chance of bacterial infection 

 against which it is extremely difficult to provide, although 

 the men are supplied with first-aid appliances of the best 

 description. As a result, it is a point for discussion whether 

 an aseptic or antiseptic method of dealing with wounds is, 

 under such conditions, the more efficient. There is much 

 reason to expect that the methods of Lister and antiseptic 

 methods in general will have to be reintroduced, and that 

 these may prove, after all, to be the soundest and most 

 practical when dealing with infected wounds. 



Bacteriological investigations are now in full working 

 order at the front, and field laboratories are provided, 

 well equipped in every respect for efficiently carrying out 

 their diagnostic work. There are a large number of organisms 

 that have to be provided against, and some few of these 

 are illustrated here. Microscopists have not of necessity 

 a collection of bacterial preparations at their disposal, and 

 it is for this reason that the photo-micrographs accompany- 

 ing this article have been reproduced. They by no means 

 represent all the organisms that will be met with, but they 

 are at least a fairly representative series. 



Description of Figure 71. 



a — Staphylococcus pyogenes aureus. x 1500. A 



spherical organism, about 0-75(ii in diameter, 

 which stains easily with all aniline dyes. It is 

 the commonest of all organisms met with in 

 suppurative conditions, such as abscesses and boils, 

 and is present normally on the skin, in the mouth, 

 and even in the air. 



b — Streptococcus pyogenes. x 1500. Occurs in chains, 

 each individual organism being from 0-75 to 

 l;x in diameter. It stains well w-ith all aniline 

 dyes. Fission takes place in one direction only ; 

 hence the chain formation. The chains vary in 

 length, and may be modified by cultivation. It 

 occurs in inflamed conditions, in gangrene, and in 

 acute abscesses, and is also the cause of erysipelas. 

 There are several varieties of the organisms, 

 but they are verj' closely allied. 



c — Streptococci in pus. x 1000. 



d — Streptococci in milk, x 750. 



e — Bacillus tuberculosis in giant cell. x 750. .\ 

 slender rod with rounded ends, which has a beaded 

 appearance when suitably stained. It does not 

 stain well with aqueous solutions of dyes. Its 

 growth in artificial cultivation is very slow, 

 several weeks being required at 37° C. Man is 

 attacked at all age-periods with tuberculosis, 

 its manifestations differing somewhat at varying 

 stages of development. It is not an immediate 

 accompaniment of the early stages of war, but is 

 only too likely to occur at a later stage in those 

 who have become enfeebled by exposure or un- 

 avoidable privation. 



/ — Tube cultivation of Bacillus tuberculosis. Natural 

 size. Three months' growth. 



g — Phagocytosis. x 750. The leucocytes in the blood 

 stream ingest any bacteria present, and so rid the 

 body of the infection. 



Ii — Micrococcus Meningitidis. x 1000. Occurs as single 

 'cocci or as diplococci within the leucocytes. It 

 stains well with ordinary dves, and grows freely 

 at 37° C. on suitable culture media. It is the 

 specific cause of epidemic cerebro-spinal menin- 

 gitis, commonly known as " spotted fever." 



Description of Figure 72. 



i — Bacillus tuberculosis in sputum, x 1500. 



y — Diplococcus pneumoniae. Pure cultivation. X 1500. 

 It retains its vitality on ordinary culture media 

 for but a short period. It stains readily with 

 ordinary aniline dyes and by Grams method. 



/t — Bacillus tetani. x 1500. A straight rod with 

 rounded ends, which forms spores freely. The 

 spores are frequently present in the dejecta of 

 cattle and horses, and in the earth, so that wound- 

 infection from this source is an ever-present 

 danger. 



/ — Bacillus typhosus. Pure cultivation. x 1500. 

 m — Spirillum cholerae Asiatica. Pure cultivation. 

 X 1 500. Curved rods, 1 to 2/j. in length, sometimes 

 forming a half-circle. Often referred to as the 

 " comma bacillus." 



n — Bacillus typhosus, showing flagellae. x 1000. 



o — Diplococcus pneumoniae. Film preparation of 

 blood. X 1000. 



p — Bacillus diphtheriac. x 1000. 



PHOTOGRAPHY. 



By Edgar Senior. 



MAKING NEGATIVES FROM BLACK AND WHITE 

 ORIGINALS. — It is sometimes required to copy pen-and- 

 ink drawings, printed matter, and so on, and to obtain 

 negatives that will yield proofs in pure black and white, 

 in which case the deposit on the plate, which corresponds to 

 the high lights, must have great opacity, while the shadows 

 or lines must be repi'esented by clear glass. To those who 

 are accustomed to the manipulations connected with the 

 wet collodion process the production of the requisite type 

 of negative would not present much difficultv, since the 

 intensification required in order to gain the necessary- 

 opacity is both quickly and easily accomplished. In the 

 case of gelatine dry plates, although there are a number of 

 ways of intensifying the image taken upon them, the time 

 occupied in the manipulations is much longer, as more 

 thorough washing is required between each operation ; 

 but even then the shadows, as a rule, are not represented 

 by the clearness of collodion. There is a deposit which it 

 is difficult to get rid of which increases as the opacity grows, 

 especially if a full exposure has been given ; and if the 

 exposure has been short it is difficult to intensify with any 

 degree of satisfaction. Thus, chiefly owing to the greater 

 sensitiveness of the gelatine plate, a sUght action takes place, 

 and a small deposit is formed over those portions of the film 

 which should be perfectly transparent. One of two things, 

 therefore, remains to be done : either to make the best 

 we can of the conditions as they stand, or to use such means 

 as will modify the results it is desired to obtain. Adopting 

 the latter course, the first thing that should be done is to 

 employ a process plate and give a full exposure, but without 

 in any degree over-exposing, and use a strong source of light 

 whenever possible for the illumination of the original. For 

 development the ordinary pyro-soda developer with an extra 

 quantity of bromide has been found to answer well in prac- 

 tice. The development of the image, however, niust be 

 \'ery carefully watched, and at the first appearance of any 

 cloudine--s the negati\'e must at once be placed (without 

 washing) into a dish containing a solution of citrate of soda, 

 of a strength of about fifteen grains to the ounce of water; 



