Imágenes de páginas
PDF
EPUB
[ocr errors]

formerly characteristic of these laboratories naturally experienced changes in regard to fittings, etc. The influence of the individual opinion of different managements also contributed to these changes. For the following description, which comprises only the biological part and not the chemical, we have taken as a pattern sometimes the Carlsberg laboratory, sometimes certain brewery laboratories fitted up for purely practical purposes, which the author has had an opportunity of inspecting; brewing is chosen by preference to exemplify the application of the methods in practice. In general this description applies also, as may be supposed, to those laboratories which are associated with other branches of the fermentation industry.

I.-FITTINGS AND APPARATUS.

1.General Principles for fitting up the Laboratory.

In many cases, when a laboratory of the physiology of fermentation has to be fitted up, the site will have been fixed so that there is no choice; the best has therefore to be done with the space at one's disposal. If there is any choice in the matter, a site facing the north is to be preferred, as sunlight is not only very troublesome in microscopical work, but is also fatal to most micro-organisms. Further, it is also very much to be recommended in cases where there is sufficient room, that the space be divided in such a way that there is a small room to be used only for work with yeast and bacteria, and a larger one in which are placed the microscope table, cupboards for cultures and apparatus, a working bench, etc.; work on moulds, for example, might be performed on the last named. The conidia of moulds, being developed on the exposed surface of the nutrient medium, cannot be retained by the liquid, and, on account of their lightness, are very easily carried about by the air from place to place. Special precautions are therefore necessary when working with moulds; the best way is, as said before, not to work with moulds in the same room where yeast and bacteria are being studied.

It is therefore necessary to provide a place as free from dust and germs as possible. For dust always contains germs of micro-organisms-of bacteria as well as of moulds and yeasts. The surface of all fittings in the laboratory should therefore be as smooth as possible, without projecting corners or hollows in which dust can settle. There ought to be at hand no more apparatus than is absolutely necessary; cultures and apparatus should therefore usually be kept in cupboards; only those objects should stand on the tables which are being used at the time, and these should be put away again after use. Only in this way is it possible to keep everything dust-free and clean. The laboratory should appear as if nothing were being carried on even at the time when most is being done. If such a system is once introduced into the working of a laboratory time is economised and security is ensured during the progress of experiments.

Cupboards and drawers ought therefore to close tightly so that dust cannot force its way in ; this is attained by providing the cupboard doors and the drawers with overlapping edges. A suitable height for the working table is 97 centimetres (about 38 in.).

Preparation of Bench Surfaces. The working tables must be prepared so that they can stand washing with spirit, as many experiments have to be performed on a wet bench. This can be done in the following way: two solutions are prepared, (l) an almost saturated solution of aniline hydrochloride in water, and (2) a solution of 1 part of potassium chlorate and 1 part of copper sulphate in 120 parts of distilled water. Solution (1) is first rubbed into the wood

and then solution (2), the solutions being used alternately until the wood has become sufficiently black. The one solution must have soaked into the wood before the other is applied. If the aniline salt partially crystallises, the bench must be moistened with warm water before solution (2) is applied. If it is found from the colour of the wood that one of the solutions has been used in excess, the other solution is applied twice successively. As a rule it is better not to use too much of solution (2), as in this event the wood becomes green instead of black. When this treatment of the bench is complete the wood is well rubbed for some time with linseed oil varnish. Repeated washings with lukewarm water will often be necessary, especially if the colour rubs off.

The above described preparation was much used formerly, but there are also other means for producing such a surface. From experiments made by the author the following recipe seems better than the first. Two solutions are also used in this method, viz.: (1) 600 grams of aniline hydrochloride are dissolved in 4 litres of water, and (2) 86 grams of cupric chloride, 67 grams of potassium chlorate, and 33 grams of ammonium chloride are dissolved in 1 litre of water. Immediately before use, 4 volumes of solution (1) are mixed with 1 volume of solution (2), and the wood is treated with this mixture once a day for four or five days. Afterwards the bench receives an application of the linseed oil varnish. The black colour develops more quickly than by the former process.

Solutions for Washing the Bench during Work.The mixture of spirit to be used for washing the bench consists of 66 parts of boiled water and 33 parts of concentrated spirit. The sponge used in washing the table is kept in the mixture when not in use. In some laboratories an aqueous solution of mercuric chloride (1 gram per litre) is used instead of spirit.

The Microscope Table.— The microscope table is most conveniently situated when facing the north. The proper height of the table is about 86 centimetres (about 34 in.), that of the stool belonging to it 62 to 63 centimetres (about 24 in.).

The Sterile Room. It is especially desirable, as stated above, to fit up a small room where only experiments with yeast and bacteria are performed. The Carlsberg laboratory has two such "sterile” rooms. The windows, which are double, are well sealed so that no draught can set the air of the room in motion. Where the windows do not look to the north, the panes are of frosted glass or are painted over. Curtains are absolutely to be avoided. The walls and the ceilings are painted with enamel which gives a perfectly smooth surface and also resists moisture; this is of importance when these surfaces have to be washed down or if special precautions have to be taken, as, e.g., when the air in the room is to be made very damp in order to purify it, the germs floating in the air being then precipitated. This is accomplished by keeping the room full of water spray for some time by means of a small sprayer, after which the room is left quiet before it is used. The floor is covered with linoleum so that all cracks and clefts are covered. Pipe systems in the room are avoided; the gas pipe just passes through the wall and ends in a stopcock to which rubber tubing is attached leading to the Bunsen burner on the working table. In addition to the latter there is a small table furnished with drawers above and cupboard below containing spatula, forceps, inoculating needles (brass rods or pieces of platinum wire fused into glass rods), and also a selection of the nutrient liquids most used and empty sterile flasks.

In working with flasks a Bunsen burner is used which can be made luminous or non-luminous and gives a large or small flame.

To complete the equipment of the room, a shallow dish of tinned copper is required. This is used sometimes when working with a Pasteur flask, sometimes for holding the sterilised spatulas or inoculating needles which are set to cool here after sterilising in the flame, the dish being covered with a glass plate sterilised in the same manner.

2.-Hansen's Sterile Cupboard. If the circumstances are such that a sterile room cannot be obtained, we must avail ourselves of the Hansen “sterile

[graphic][merged small]

cupboard ” and perform the finer kinds of work in it. This cupboard was the model for fitting up the sterile room, and is really a miniature of the latter. It is obvious that the cupboard ought also to be used when it is desired in particularly delicate work to take special precautions against infection.

This cupboard (Fig. 1) consists chiefly of glass, only the framework and floor being mahogany. The latter is smooth, and is polished with linseed oil varnish, and bears washing

« AnteriorContinuar »