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to possess ascus fructification. Some are similar to Dematium pullulans, and some investigators (e.g., Laurent) have, for this reason, classed Cladosp. herbarum and Demat. pullulans in the same development series. Lopriore has studied a parasitical Cladosporium herbarum form occurring on wheat, which forms sclerotia. He states that it produces Hormodendron cladosporioides as well as Demat. pullulans. It is therewith stated that several species occur that produce conidial forms, which can be identified with the species referred to above.

IL-FISSION FUNGI (SCHIZOMYCETES).

General.

1.-STRUCTURE AND FORM OF BACTERIAL CELLS.

The Cell Contents.-Like yeast cells, the bacterial cell consists of a mass of protoplasm surrounded by a membrane. It has been contended as to whether it contains a cell nucleus or not. Later investigations, however, show that in this respect also bacterial cells resemble other cells.

As with yeast cells, vacuoles and granules occur in the protoplasm. In some bacteria a substance is found which is probably granulose or an allied carbohydrate, as it is stained blue by iodine. Sulphur granules or oxide of iron are found in other forms; occasionally fat globules are observed, especially in the cells of old cultures. Colouring matter is found in many species, often in such quantity that the colonies are highly coloured, e.g., red, yellow, blue, violet, brown, etc. The colouring matter is found partly in the interior of the cells, and partly secreted as granules lying between the cells.

The Cell Wall and its Gelatinous Formation.. If the cell is placed in a solution of common salt, the

plasma separates from the membrane so that the latter becomes plainly visible. This phenomenon is called plasmolysis. The membrane does not consist of cellulose but of albuminoids, probably modifications of those forming the protoplasm. The membrane often possesses the property of forming gelatine and swells up. The growths are then enveloped in mucilage and form gelatinous films or masses, called Zooglom (Fig. 133). In some species the mucilage is stained blue by iodine, in others it gives the cellulose reaction (blue stain by iodine in zinc chloride or iodine and sulphuric acid).

[graphic]

FIG. 133. Bacterium Pasteurianum, Hansen. Gelatinous formation in an old growth on beer. The three cells to the left have fallen out. The cells are prepared and stained by Löffler's method. 19. (After Hansen.)

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Flagella. Many bacteria are observed under the microscope to be in motion; this motion is often due to physical causes and is then the so-called Brownian molecular movement. Another kind of movement is effected by special organs of motion, flagella or cilia. The rapidity which this motion attains, has, with some species, an average value of about mm. per second. The flagella or cilia were discovered in 1836 by Ehrenberg, and, as a rule, can only be observed after a special preparation (see p. 91). In some forms they are found at the poles of the cells, in others at the sides: occasionally several are found to

gether. Alfr. Fischer distinguishes between bacteria (1) with one flagellum at the end (Fig. 135), (2) with a cluster of flagella at the end, and (3) with flagella over the whole surface (Fig. 134). Flagella furnish important characteristics for the determination of species, and for classifi

a

FIG. 134.-Clostridium butyricum, Prazmowski.

Butyric acid bacterium with

flagella. a, Vegetative motile cell; b, sporulating motile cell. 139. (After Alfr. Fischer.)

cation it is of importance to determine if the species concerned occurs with flagella or without.

Bacteria with flagella movement are called motile. This motion may be temporarily stopped by certain means, e.g., by an increase in the acid content of the nutrient medium or by a deficiency of oxygen; the condition of the organism

FIG. 135.--Termobacterium aceti, Zeidler. Acetic acid bacterium with one flagellum. 120o. (After Zeidler.)

By

is then known as flagella-stiffness (Geisselstarre). neutralisation or by aëration the stiffness can again be removed. When, therefore, bacteria in a culture do not move just at the instant, one cannot be always certain that the power of motion has altogether left them. Various sub

stances can attract or repel motile bacteria; this property is known as positive or negative Chemotaxis.

Shape of the Cell.-Some of the cell shapes which occur most frequently are as follows: Spherical bacteria are

[blocks in formation]

FIG. 136.-Form and size of various bacteria. A, 1. Micrococcus of various sizes. 2. Diplococci. 3. Streptococci. 4. Micrococcus tetragonus. 5. Sarcina ventriculi, package form. 6. Staphylococci. B, 1, 2, 4. Long rods. 3. Short rods. 5. Connected chains of long and short rods. 6. Long threads. 5. (4, 5. 799.) (After P. Baumgarten.)

known as cocci (Fig. 136, A), rod-shaped ones, i.e., those which are at least double as long as they are broad, as bacilli or long rods (Fig. 136, B, 1, 2, 4, 5), and those of which the length and breadth are more nearly equal, as bacteria

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(in the true sense) or short rods (Fig. 136, B, 3, 5). Bacillus displays (as the result of spore formation) a more or less decided club shape it is called Clostridium (Fig. 137): if curved it is called Vibrio, and if it is screw shaped, Spirillum. The very long thread-like bacteria are known as Cladothrix, Streptothrix, Crenothrix, etc. It is common for the same species to occur in different forms.

The smallest

Most bacteria are very small, and a powerful magnification is required in order to observe them. cells are not more than 1 μ long. Especially large forms are, e.g., Bacillus oxalaticus, whose rods may be 30 μ long and 4 thick, and Bacterium megatherium, whose rods are 10 μ long and 2.5 μ broad.

2. METHODS OF REPRODUCTION.

Cell Fission. As above mentioned, the vegetative multiplication of bacteria proceeds by division or fission; many forms have only this one method of multiplication, whilst others can, in addition, form endospores. Rod bacteria become elongated, and divide by means of a septum; the latter never occurs lengthways; spherical bacteria do not alter their original appearance before division has taken place. In the latter, division can take place in several directions. The new-formed cells often remain in union with the mother cells, whereby long chains may be formed.

By seeding on various nutrient gelatines the species produce colonies, which have a more or less varied macroscopical appearance, as regards both shape and condition of the surface (slimy, dry). In this connection the method by which the colonies were started is also of influence, whether it was by stab or streak cultures or giant colonies from the seeding of a drop. It has already been said that the colour of the colonies may vary.

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