. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. VARIABILITY OF GELATIN. 31 said, is added to certain table gelatins to increase their body. Gelatin also contains a variety of decomposition products due to the growth in it of various fungi and bacteria while it is in the vats or in the drying-house. If there is any delay in the drying it is spotted all over with molds and bacteria. It also contains some wax or grease, used to anoint the surface on which it is spread to dry, and this wax or grease is probably also a varial)le sulxstance. Gelatins also polarize, it is said
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. VARIABILITY OF GELATIN. 31 said, is added to certain table gelatins to increase their body. Gelatin also contains a variety of decomposition products due to the growth in it of various fungi and bacteria while it is in the vats or in the drying-house. If there is any delay in the drying it is spotted all over with molds and bacteria. It also contains some wax or grease, used to anoint the surface on which it is spread to dry, and this wax or grease is probably also a varial)le sulxstance. Gelatins also polarize, it is said, in many different ways. An absolutely pure gelatin of uniform character for bacterio- logical purposes is not to be had. That which perhaps comes the nearest to it and which is here recommended is Nelson's gelatin, made in London and well known to the makers of photographic dr}-plates, who use it in large quantities. It comes in two grades, a hard and a soft, and costs about # per pound. No. i, that which I like best, comes in shreds resembling " excelsior " used for packing (fig. 28). No. 3, which comes in long, broad strips, contains nuich cell detritus, etc., and filters with difficulty. Other expensive gelatins, said to be of quite uniibrm quality, are. Fig. 19* Lichtdruck gelatin, made b}- Carl Creutz, Michelstadt, in Hesse, and Geneva Red Cross gelatin made by Winterthur, in Switzerland, under direction of Dr. Eder, of the Imperial Institute of Vienna (Cockayne;. Nutrient Agar. Ao'ar, or agar-agar, as it is usually called, from a Malay word meaning "vege- table " is a manufactured product obtained from various sea-weeds growing in Chinese and Japanese waters. Various species are used as food and the trade is con- siderable. It usually comes into the hands of the bacteriologist as long, slender, )'ellowish-white strips (fig. 29) or as blocks (fig. 30), or more especially in recent years, in the form of a gray-white fine powder of European manufact
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