192 



KNOWLEDGE. 



May. 1911. 



often develop vacuoles, and assume varied shapes. They 

 all stain easily by most of the well-known bacteriological 

 staining methods, and in most, if not all cases, a flagelluni 

 or fiagella may be demonstrated. 



Figures 4 and 5 show the marked differences that occur 

 in some species under different methods of cultivation 

 (Pliotobacteriiim bttlticniuK Figure 4 is grown on a 

 fluid fish-broth medium. Figure 5 is grown on peptoue- 

 beef-broth containing the maximum amount of saline matter 

 that the organism will tolerate. In each case fiagella are 

 clearly shown. 



The question whether the organism itself produces light as a 

 direct metabolic process, or whether it is an extra-cellular 

 bacterial product that is light-producing, is still an undeter- 

 mined point ; but all the evidence goes to show that the light 

 production is undoubtedly associated with the life-history of 

 the organism. By no experimental means has it as yet been 

 possible to isolate the light-producing material from the 

 actively-li\ing cell. 



These organisms may be recommended to the amateur 

 microscopist as a most fascinating field of research, in which 

 there are still many problems to be solved ; they present no 

 great cultural difficulties, nor do they re(juire the resomxes of a 

 bacteriological laboratory in which to carry them out. 



J. Edwi.v B.\rnakd. F.K.M.S. 



KO\AL MICKt>SCOPIC.-\L SOCIETY.— March 15th. 

 1911. Mr. H. G. Plimtner, F.K.S.. president, in the chair. 

 Dr. Ralph Vincent gave a lantern demonstration on " Some 

 Photomicrographs illustrating the morphology of the organisms 

 concerned in the production of acute intestinal toxaemia in 

 infants." These included Bacillus sKbtilis. B. iiicsciifcriciis. 

 '■ No.7,"B. iiiescntcriciis viilgatiis. and B.protciis vulgaris. 

 The photographs showed the organisujs stained, unstained and 

 during life. Photographs were also shown of Streptococcus 

 lactictts. Bacillus acidi lactici and B. huli^aricus. 



Mr. F. \V. Watson Baker contributed a paper on "".\nomalies 

 in Objective Screw Threads." 



Mr. E. M. Nelson described a new piece of apparatus con- 

 sisting of an objective mount fitted with an iris diaphragm, in 

 which the iris was just clear of the back lens, and its mo\'e- 

 meut was controlled by a collar adjustment. This piece of 

 apparatus would no doubt be of great value to workers who 

 employ dark -ground illumination for viewing bacteria, and so on, 

 as in many instances, owing to defects in the illuminator, it was 

 not possible to obtain a dark field when the objective had a 

 wide an.gle. This fault was remedied by stopping down the 

 aperture of the objective by means of the diaphragm. Mr. 

 Nelson also described some new objectives and eye-pieces 

 made by R. W'inkel, of Giittingen, and contributed a short 

 historical and descriptive resume of the "Variable Microscope." 



Mr. J. Murray brought forward a Report on the Rotifers 

 collected by the British .-Vntarctic Expedition of 1909. 

 Forty-six Bdelloids were collected, bringing the AustraUan 

 list up to fifty-four species. There were seven new 

 species, and ei.ght others occurred as distinct varieties. 

 The new species were Plulodina australis. Callidina 

 arinillafa. C. lepida, C. longistyla. C. scrrulata, C. 

 iiiirahilis and Habrotrocha straiigulata. The most 

 aberrant form was C. iiiirabilis. which had peculiar 

 fleshy processes on the trunk. The rotifera fauna of the 

 Australian Alps resembled that of Britain. The arid low- 

 lands were very unproductive. Three-fourths of the species, 

 and all the new species, occurred in the Blue Mountains. 

 at moderate elevations. Eight species of non-Bdelloid rotifera 

 were also noted from the water supply and ponds in Sydnev. 



THE PREVENTION OF FADING OF ANILINE 

 STAINED MICROSCOPIC PREPAR.ATIONS.— Incommon 

 with many microscopists I ha\e found that films of blood, 

 bacteria, and so on. when stained with almost any of the 

 aniline dyes, fade after a time when mounted in Canada 

 Balsam. This is especially the case with methylene green, 

 thionin, methylene blue, or methylene blue and eosin, either 



separately or combined as Jenner's stain, and all the modifica- 

 tions of Rouuinowskv's \aluable stain, e.g.. Giemsa, Leishmann, 

 ^^"right. 



There is no doubt but that the cause of fading in balsam- 

 mounted preparations, judging from my own experience and 

 from the expression of the opinion of numerous authorities on 

 the subject, is acidity whether present at the time of mounting, 

 or developing subsequently from oxidation of the mounting 

 medium. 



I will not enter into details of my experiments or the state- 

 ment of the authorities as to the facts which lead me to the 

 above conclusion. They have been described in full elsewhere. 

 Lancet. 1911, Vol. I, page 876. 



It may. I think, be stated that practically all substances of 

 the nature of balsams, oleo-resins or cedar oil will sooner or 

 later oxidise and become acid and, therefore, are liable to cause 

 fading of the aniline stains. 



It is not possible to obtain .a neutral Canada Balsam that 

 will remain neutral. 



.■\fter numerous trials. I have found that I'araftinuin 

 liquiduin is a neutral medium w^hich does not undergo 

 oxidation and. therefore, does not become acid. 



I have used a pure form of liquid paraffin, namely 

 Burroughs and W'ellcome's " Parolein " and so far have found 

 the results admirable. It is more trouble to mount in than a 

 balsam, and the preparations require to be ringed or 

 cemented round with some cement which is also neutral. 

 The following is the method I use for mounting films of blood 

 or bacteria which are spread and stained on the slide. 



.•\ perfectly cleaned cover-glass is held in a pair of forceps 

 over the flame of a spirit lamp for a second or two to drive off 

 any moisture on the glass, and is then laid on a clean sheet of 

 notepaper. .A very small drop of Parolein is placed on the 

 centre of the cover-glass, and the slide with the blood film, 

 after being shghtly wanned over the flame, just enough to be 

 sure that the glass is perfectly free from moisture, is gently 

 let down on to the cover-glass. In a second the oil has run 

 nearly to the margins by capillarity, and a little pressure on 

 the cover-glass will send it completely to the margins. If the 

 amount of oil is just sufficient to reach the margin of the 

 cover-glass so much the better. If there is too much oil, 

 the preparation is placed under a piece of blotting 

 paper and the excess of oil pressed out as much as possible. 

 One soon learns how much oil is required to make a clean 

 preparation. .A not uncommon thing is to find that the cover- 

 glass rocks, that the oil has only covered about three parts of 

 the square or circle. This is almost always due to the presence 

 of a minute particle of dust between the cover-glass .and slide, 

 and is to be prevented by seeing that the co\er-glass is quite 

 clean and free from dust before placing the oil on it, and by 

 just dusting gently the film surface on the shde. But usually 

 it is easily remedied by running in a \ery small drop of 

 Parolein at the margin of the coverglass. 



To fix the cover-glass in position it is necessary to ring it 

 round with some cement. The cement must be neutral or 

 there will be fading, and the cement must withstand the action 

 of the immersion cedar oil. I first ring round the preparation 

 with .-Vpathy's Cium Syrup made as follows: Picked gum 

 arable, cane sugar not candied, distilled water, of each, 50 

 grammes. Dissolve over a water bath and add 0-05 grammes 

 of thymol. I test the reaction with litmus paper, and if acid 

 I add a few drops of a solution of Sodii carbonas. If the 

 cover-glass is round the cement can easily be applied on a 

 turntable : if square, which I prefer, one paints it round with 

 a \ery small brush. This sets in about fifteen to thirty 

 minutes in a w-arra Toom. When dry I apply o\er it a coat of 

 Bell's cement, which also dries quickly. 



I should be glad to hear of any better cement, but wh.atever 

 be its nature it must be neutral in reaction. 



As regards the optical characters of Parolein, the refraction 

 index is 1 -471. That of solid Canada Balsam 1 -538, that of 

 balsam in xylol a little lower, say 1 • 530. The refraction 

 index of bacteria is s;iid, according to .A. Fischer, to be 1-55. 



