Nov. 1 6, 1888.] 



SCIENTIFIC NEWS. 



5i3 



Avoid as far as possible all fingering or pulling of the 

 parts. Epithelium, in particular, must never be rubbed, 

 however lightly. Wide- mouthed stoppered bottles are 

 used in all the operations with fluid ; those which have 

 contained chromic acid must be scrupulously washed 

 with strong mineral acid and water before they are 

 used for any other purpose. 



The next step is to remove all free chromic acid, and 

 gradually to dehydrate the tissues. Different strengths 

 of alcohol are employed. Buy a gallon of methylated 

 alcohol of good strength, and a few ounces of absolute 

 alcohol. The methylated alcohol should contain 80 per 

 cent, of spirit. Mix it with water so as to get a 40 per 

 cent., and also a 60 per cent, solution. Then remove 

 the tissues from the chromic acid, add to them a small 

 quantity of 40 per cent, alcohol, pour this away, and add 

 a relatively large quantity of the same. After 24 

 hours change to 60 per cent., and renew the fluid once or 

 more, according to the size of the tissues and the amount 

 of colouration of the alcohol. Then change to methylated 

 alcohol of full strength. If the tissues are not immedi- 

 ately wanted, keep them in methylated alcohol. Too 

 long soaking in absolute alcohol renders them brittle and 

 over-contracted. The gradual saturation with strong 

 alcohol should occupy about a fortnight. Note that 

 waste alcohol should be kept for redistillation. 



All is now ready for staining. Here, again, it is best 

 to practise one method only until proficiency has been 

 gained. Begin with alcoholic borax-carmine, and stain 

 the tissues whole before cutting. The staining fluid is 

 made in this way : Take a 4 per cent, solution in water 

 of borax. Saturate with carmine (2 to 3 per cent), 

 leaving the mixture to stand for a day or two, and stir- 

 ring now and then. Add an equal bulk of methylated 

 alcohol. Let the solution stand for a week,'and then filter. 

 Place the tissues in perfectly clean bottles, with 

 enough of the staining fluid to cover them. Leave them 

 for two or three days, then pour off the fluid, and add 

 methylated alcohol, slightly acidulated (two drops of 

 hydrochloric acid to the ounce). The crimson stain is 

 thereby fixed, and brightened in colour. Transfer once 

 more to ordinary methylated alcohol, and just before 

 cutting to absolute alcohol for twenty-four hours. 



Most tissues require imbedding to give sufficient firm- 

 ness. For cutting by hand nothing is better than cacao 

 butter. Make a small rectangular paper tray, about 

 1 in. long, I in. wide, and h in. deep. Fill this with the 

 melted cacao butter, dry the tissue superficially, and 

 place in the tray. Take care that it is completely im- 

 mersed in the butter, and don't heat the butter more 

 than is absolutely necessary. When the preparation is 

 cold remove the paper, and pare down the block with a 

 sharp knife. It is undesirable to have to cut through 

 much of the imbedding substance with the razor, and 

 equally undesirable to weaken the block too much. The 

 top of the block must therefore be trimmed so as to slope 

 away on all sides, and the operation must be repeated 

 frequently as cutting proceeds. To prevent melting in 

 the hand hold the block in a piece of paper. Use the 

 sharpest razor you can obtain, wet the blade and also 

 the tissue with methylated alcohol, pick up the sec- 

 tions as cut with a small camel-hair brush, and 

 transfer to a watch-glass of methylated alcohol. 

 When a sufficient number have been obtained pick 

 away and remove the chips of imbedding substance 

 with a needle and brush, replace the methylated alcohol 

 by absolute, and this again by oil of cloves. Finally 



pick out the sections one by one with a section-lifter, 

 and mount in balsam. 



Where a mechanical microtome is required Fearnley's 

 may be recommended. It is good and cheap, and admits 

 of imbedding either in a waxy medium or in celluloidin. 

 Special instructions are required for this or any other 

 mechanical microtome. Caldwell's rocking microtome 

 is indispensable where many consecutive sections 

 are required, but it is not well adapted to the 

 wants of the beginner. It is somewhat costly, and the 

 necessary appliances, to say nothing of the continuous 

 time required by the different operations, presuppose 

 serious devotion to biological work. Hand-cutting will 

 do a great deal, and no microtome can altogether replace 

 it. The novice will therefore do well to give his princi- 

 pal or sole attention to hand-cutting for at least the first 

 few months of his initiation. 



^»tXV?- — 



THE ACTION OF MICROBIA UPON 

 COLOURING MATTERS. 



'T'HE following memoir has been submitted to the 

 Paris Academy of Sciences by its author, M. J. 

 Raulin : — 



If we colour wort in alcoholic fermentation with 

 magenta, Nicholson blue, imperial violet, saffranine or 

 Poirrier orange No. 2, a part of the colouring matter 

 is seized upon by the yeast and dyes it strongly, whilst 

 cochineal, logwood, orchil, and extract of indigo do not 

 dye it. In the former case we have a true tinctorial 

 action analogous to that which the same colouring matters 

 exert upon animal fibres. 



The spores of Aspergillus niger have been sown in 

 artificial liquids suitable for cultivation, one containing 

 nitrate of ammonia ; a second, a salt of aniline ; a third, 

 a salt of rosaniline ; a fourth, extract of indigo ; the fifth 

 being entirely free from nitrogen. The mould flourished 

 well in the first liquid, but gave merely an insignificant 

 yield in the four others. It will be remembered that M. 

 Pasteur has found moulds able to assimilate the nitrogen 

 of ethylamine, and that M. G. Ville has observed large 

 plants assimilating the nitrogen of ethylamine and 

 methylamine. Are these differences of action connected 

 with the differences of constitution of compounds belong- 

 ing respectively to the aromatic and to the fatty series ? 



Yeast-water, beer-wort, or an artificial sugary liquid, 

 slightly acidified if tinted with extract of indigo, are 

 slowly and progressively decolourised in a few days in 

 the absence of any organism, but in presence of air. 

 This is an oxidation, since carbonic acid gas hinders the 

 decolouration. Certain aerobic organisms, such as 

 Aspergillus niger, Mycoderma vini, Mycoderma aceii, 

 hinder or retard this decolouration by opposing the access 

 of oxygen. Active beer-yeast produces the same effect ; 

 still, after some weeks, beer-wort in active fermentation 

 by means of ordinary brewers' yeast, if tinted with 

 extract of indigo, is decolourised in the absence of 

 atmospheric oxygen, but this is a reduction by hydro- 

 genation, for the colour reappears on the contact of air, 

 and this reduction coincides with the development of 

 microbia, similar to the lactic ferment. 



To render this decolouration of extract of indigo by 

 reduction as certain and as rapid as possible, the yeast- 

 water is left to itself for some days at a temperature of 

 about 75 Fahr. It is then full of bacteria, and gives off 

 a putrid odour. The bacteria increase rapidly if they 

 be sown in fresh yeast-water. 



