XX. THE STUDY OF THE PATHOGENIC BACTERIA.

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The student, who has conscientiously worked out the methods, etc., previously dealt with, is in a position to make accurate observations and to write precise descriptions of the results of such observations. He is, therefore, now entrusted with pure cultivations of the various pathogenic bacteria, in order that he may study the life-history of each and record the results of his own observations—to be subsequently corrected or amplified by the demonstrator. In this way he is rendered independent of text-book descriptions, the statements in which he is otherwise too liable to take for granted, without personally attempting to verify their accuracy.

During the course of this work attention must also be directed, as occasion arises, to such other bacteria, pathogenic or saprophytic, as are allied to the particular organisms under observation, or so resemble them as to become possible sources of error, by working them through on parallel lines—in other words the various bacteria should be studied in "groups." In the following pages the grouping in use in the author's elementary classes for medical and dental students and for candidates for the Public Health service is adopted, since a fairly long experience has completely vindicated the value and utility of this arrangement, and by its means a fund of information is obtained with regard to the resemblances and differences, morphological and cultural, of a large number of bacteria. The fact that some bacteria appear in more than one of these groups, so far from being a disadvantage, is a positive gain to the student, since with repetition alone will the necessary familiarity with the cultural characters of important bacteria be acquired. The study of the various groups will of course vary in detail with individual demonstrators, and with the student's requirements—the general line it should take is indicated briefly in connection with the first group only (pages 410-411). This section should be carefully worked through before the student proceeds to the study of bacterioscopical analysis.

It is customary to commence the study of the pathogenic bacteria with the Organisms of Suppuration. This is a large group, for all the pathogenic bacteria possess the power, under certain conditions, of initiating purely pyogenic processes in place of or in addition to their specific lesions, (e. g., Bacillus tuberculosis, Streptococcus lanceolatus, Bacillus typhosus, etc.). There are, however, a certain few organisms which commonly express their pathogenicity in the formation of pus. These are usually grouped together under the title of "pyogenic bacteria," as distinct from those which only occasionally exercise a pyogenic rÔle.

The organisms included in this group are:

1. Staphylococcus pyogenes albus.
2. Staphylococcus pyogenes aureus.
3. Staphylococcus pyogenes citreus.
4. Streptococcus pyogenes longus.
5. Micrococcus tetragenus.
6. Bacillus pyocyaneus.
7. Bacillus pneumoniÆ.

and in certain special tissues

8. Micrococcus gonorrhoeÆ.
9. Micrococcus intracellularis meningitidis (Meningococcus).
10. Micrococcus catarrhalis.
11. Bacillus Ægypticus (Koch-Weeks Bacillus).

The group may with advantage be subdivided as indicated in the following pages:

I. Pyogenic cocci.

Staphylococcus pyogenes albus.
Staphylococcus pyogenes aureus.
Staphylococcus pyogenes citreus.
to contrast with
Micrococcus candicans.
Micrococcus agilis.

1. Prepare subcultivations from each:

Bouillon, }
Agar streak, }
Blood serum, }
Litmus milk. } and incubate at 37°C.
Agar streak, }
Gelatine stab, }
Potato. } and incubate at 20°C.

Compare the naked-eye appearances of the cultures from day to day. Note M. agilis refuses to grow at 37°C.

2. Make hanging-drop preparations from the bouillon and agar cultivations after twenty-four hours' incubation. Examine microscopically and compare. Note the locomotive activity of M. agilis and the Brownian movement of the remaining micrococci.

3. Prepare cover-slip films from the agar cultures, after twenty-four hours' incubation. Stain for flagella by the modified Pitfield's method. Note M. agilis is the only micrococcus showing flagella.

4. Make microscopical preparations of each from all the various media after twenty-four and forty-eight hours and three days' incubation. Stain carbolic methylene-blue, carbolic fuchsin, and Gram's method. Examine the films microscopically and compare. Note in the Gram preparation, the Gram negative character of certain individual cocci in each film prepared from the three days' growth—such cocci are dead.

5. Stain section of kidney tissue provided (showing abscess formation by Staphylococcus aureus) by Gram's method, and counterstain with cosin.

6. Stain film preparation of pus from an abscess (containing Staphylococcus pyogenes aureus) with carbolic methylene-blue and also by Gram's method, counterstained with cosin.

7. Inoculate[15] a white mouse subcutaneously with three loopfuls of a forty-eight-hour agar cultivation of the Staphylococcus aureus, emulsified with 0.2 c.c. sterile broth.

Observe carefully during life, and when death occurs make a careful post-mortem examination.

II. Pyogenic cocci.

Micrococcus gonorrhoeÆ.
Micrococcus intracellularis meningitidis (meningococcus).
Micrococcus catarrhalis.
Micrococcus tetragenus.
Micrococcus paratetragenus.

III. Pyogenic cocci.

Streptococcus pyogenes longus.
Streptococcus of bovine mastitis.
Streptococcus lanceolatus (Diplococcus pneumoniÆ or pneumococcus).
to contrast with
Streptococcus brevis.
Streptococcus lebensis.

IV. Pyogenic bacilli.

Bacillus pneumoniÆ (Friedlaender).
Bacillus rhinoscleromatis.
Bacillus lactis aerogenes.

V. Pyogenic bacilli.

Bacillus pyocyaneus.
to contrast with
Bacillus fluorescens liquefaciens.
Bacillus fluorescens non-liquefaciens.

VI. Pneumonia group.

Streptococcus lanceolatus (pneumococcus).
Bacillus pneumoniÆ (Friedlaender).
Streptococcus pyogenes longus.

VII. Diphtheroid group.

Bacillus diphtheriÆ (Klebs-Loeffler).
Bacillus Hoffmanni.
Bacillus xerosis.
Bacillus septus.

VIII. Coli-typhoid group.

B. typhi abdominalis (B. typhosus).
B. coli communis.
B. enteritidis (Gaertner).
to contrast with
B. aquatilis sulcatus.

IX. Escherich group.

B. coli communis (Escherich).
B. coli communior.
B. lactis aerogenes.
B. cloacÆ.

X. Gaertner group.

Bacillus enteritidis (Gaertner).
B. paratyphosus A.
B. paratyphosus B.
Bacillus cholerÆ suum (Hog Cholera).
B. psittacosis.

XI. Eberth group.

B. typhosus (Eberth).
B. dysenteriÆ (Shiga).
B. dysenteriÆ (Flexner).
B. fÆcalis alcaligines.

XII. Spirillum group.

Vibrio cholerÆ.
Vibrio metschnikovi.
to contrast with
Vibrio proteus (Finkler and Prior).
Spirillum rubrum.
Spirillum rugula.

XIII. Anthrax group.

Bacillus anthracis.
to contrast with
Bacillus subtilis.
Bacillus mycoides.
Bacillus mesentericus fuscus.

XIV. Acid fast group.

Bacillus tuberculosis (human).
" " (bovine).
" " (avian).
" " (fish).
to contrast with
Bacillus phlei (Timothy grass bacillus).
Butter bacillus of Rabinowitch.

XV. Plague group.

Bacillus pestis.
B. septicÆmiÆ hÆmorrhagicÆ.
B. suipestifer.

XVI. InfluenzÆ group.

B. influenzÆ.
Bacillus Ægypticus (Koch-Weeks).
Bacillus pertussis.

XVII. Miscellaneous.

Bacillus leprÆ.
Bacillus mallei.
Micrococcus melitensis.

XVIII. Streptothrix group.

Streptothrix actinomycotica.
Streptothrix madurÆ.
to contrast with
Cladothrix nivea.

XIX. Tetanus group.

Bacillus tetani.
Bacillus oedematis maligni.
Bacillus chauvei (symptomatic anthrax).

XX. Enteritidis sporogenes group.

Bacillus enteritidis sporogenes.
B. botulinus.
B. butyricus.
B. cadaveris.

FOOTNOTES:

[15] See note on Vivisection License, page 334.


                                                                                                                                                                                                                                                                                                           

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