The effects upon the body mechanism of the activities of disease-producing germs vary, of course, greatly for the different germs. Certain general modes of action may. however. be men tioned. ( ) The direct (usually local I effect of the presence of the germs. Thus. in diphtheria the direct local effect of the germ in the throat is death of parts of the mucous membrane and the formation of what is known as a false mem brane. In a similar manner the ulcers . in the intestines in typhoid fever are due to the direct local action of the typhoid bacillus. Another local effect which germs may sometimes have consists in the formation of infectious emboli in different parts of the body. Thus, for in stance, in infectious endoearditis with bacterial growth in the heart valves, a little mass of bacteria may become detached, and carried the circulation until it reaches a vessel too small for it to pass through. Here it stops, forming an infectious embolus and thus setting up a new focus of infection. (') The produc tion of toxins (q.v.). These are poisons pro duced in the body by the activities of bacteria. They seem to lie largely present in the plasma of the blood and are Consequently distrilmted throughout the body. It is to these toxins that the systemic symptoms of an infectious disease are due. e.g. the fever. prostration. delirium. etc. These toxins differ for different bacteria. a par ticular toxin probably being specific for each species of germs. That a disease may be ac cepted as positively proved to be of genii origin, it must fulfill certain very rigid conditions. tine single species of germ must always be found present in the diseases. This mast not be found regularly in connection with any other disease. It must be possible to cultivate this germ artificially, and to separate it in what is known as :i pure vulture. i.e. a growth of this germ free fiont any other living sub stan•e. It ninst he possible to induce the same to a similar disease in animals by injecting them with this pure culture. Comparatively few dis cascs yet fulfill all of these requirements. Altion.. the most important of the diseases which have hem) proved to be of germ origin mentioned anthrax, actinomycosi, _Asiatic chol era. bubonic plague. acute cerebrospinal menin gitis, diphtheria. erysipelas, glanders. gonorrlaea, influenza, leprosy, malaria. pneumonia, relapsing fever, tetanus, tuberculosis, and typhoid. tif the more important of the diseases which Iron' their behavior are believed to be of germ origin, hut in which the geniis have 1114 as yet been found, arc scarlet fever. S11111111/0.X, typhus. and wlita)ping-eough.
TEciixtquE. In many eases of disease a determination of the species of bacteria present may he made by 1111balls of a bacterial examination of pathological material during life. This is done in one of three ways: first. by cover-glass preparation; second, by culture; third, by animal inoculation. In eases a little pathological inaterbil may be ob tained on a sterilized platinum loop: in others a piece of absorbent cotton wound about a stiff wire and forming a 'swab' is used. by means of which 1/11, or exudates may be obtained and trill-1)1)1AM in a sterile test-tulie into which the swab is thrust; in still other case: fluid ma terial may he obtained by aspiration. _1 cover glass preparation is thus made: .1 very small amount of material is smeared over a cover-glass in such a way as to leave streaks of it and net a continitons layer. After being, dried by being held in the fingers, charged side uppermost, over a Bunsen burner. it is passed rapidly three times directly through the Ilaine of the burner by means of a forceps. to 'fix' it. The cover glass then held in the grasp of the forceps, charged side tip and level. and the chosen stain ing fluid is dropped on it from a dropping hot lie, till it is completely covered. The cover glass i. then heated over the flame and washed in water, and any other mbeessary processes are concluded, according to the method of staining employed. The cover-glass with the charged side down, and wet thoroughly with water, is placed on a microscopic slide, and the excess of water is removed by means of filter paper in the visual way. .1)1 oil-immersion lens is then used, for examination of the specimen.
Culture mediums differ in different cases. Potato. agar-agar. litmus-milk. glucose' agar-agar. and glucose gelatin are used: but the best culture medium for general purposes is en agulated blood serum. At the slaughter-house blood is obtained as it rolls from the vessels of the beeves, preferably that which tlo•s from the parotid artery. as it clots more plickly. The jar in which it is received is left in a cool place for twenty-four hours. .After a few honrs the clot is gently loosened from the sides of the jar, to facilitate its contraction, and after this the jar is not ngitated. After about twenty•four hours the serum is with a pipette. Three parts of blood serum and one part of gluense bouillon are mixed to form ill.' culture medium. which is run into test tubes in small quantities. The titles are ',laved in a tilted position in the hot air sterilizer and when withdrawn the serum is found to be coagulated in a slanting position. _Ilaterial obtained on a 'swab; e.g. from the throat of a suspected diphtheria patient, is light ly smeared over the exposed surface of the blood serum in a eulture-tube. The culture tube is then placed in an incubator or thermo stat, and tla- bacteria are allotted to grow on the nutrient surface. for subsequent examination with the micro-cope.
Animal inocidations are made as follows: A small piece of suspected material may he in serted under the skin of a mouse by ineans of a platinum N\ ire, or a little fluid may be injected under the skin of a guinea-pig or rabbit. .1fter the death lif the animal an autopsy is made. and various organ. and tissues are examined micro scopically.
SpLcixi. 1;:xxvtlx.vrioNs. In examining spu tum for tubercle baeilli. a cover-glass prepara tion is made from a dense grayish white particle taken from the incoming sputum. The tubercle bacillus is a slender rod varying from 1.5 micro millim•ters to 4 micromillimeters in length, and about 0.4 mieromillimeter in breadth. generally slightly curved. The bacilli occur singly, though in culture- they are sometimes found in chains of four to six links. Club-like forms and branehes have been seen aIsn, It must be dif ferentiated from the sint.;_onn bacillus, Lust garten's bacillus of syphilis, and certain others.
In examining for the bacillus of diphtheria, a 11100(1.Sert1111 culture-tube is inoculated by means of a 'swab' with exudate from the tonsils of the patient, and is placed in the inenbator for about titteen hours. The resultin". _Tomtit is examined by means of a stained cover glass preparation. .1101inted on a slide. the specimen is examined with a high-power lens. The haeilli will be found to be of vPrying size, from 1 to fi micro millimeters and 0.5 to I mieromillimeter broad. straight or slightly curved, with rounded ends, singly or in pairs. The ends may be en large 41. Irregular forms are eommon. (Misters or bundles and rarely branching forms are found. l'or the deteetion of the plasmodium of malaria, ii fresh of blood i- taken from the tubule of the ear. and received on a cover-glass• This is inverted on a se. to spread the 4peci men evenly, and all superfluous blood is removed.
may he secoired by heating, or by irn Thersing in a mixture of absolute alcohol and ether. The preparation is stained to secure con trast between the parasite and the blood-disks. Under the microscope, the plasmodicspixarabout the size of red blood-corpuscles, discoid, star shaped. in odd forms with prolongations, tlagel he and branches, nucleated, granular, etc. If not fixed, the parasites show rapid anwcboid movements in a fresh preparation. Other micro organisms are described under the titles of the diseases they cause. Consult: FriedIiinder, Mi kroskapis•he Technik (Berlin, 1901)) : Thoma, /ehrbuch der pathologiRchoi nat oin ie. trans. by Bruce (London, 18961; ()thither. Bakteriologie (Leipzig, IS9S) ; Abbott, Principle• of Bacteriol ogy (Philadelphia, 1S9S) ; Mallory and Wright, Pathological Technique (Philadephia, 1,198) ; Lehmann and Neumann. Bakteriologische Diag tiost ik 1S913): Steinberg, Bacteriology (New York, 1901) : Park. Bacteriology (New York and Philadelphia, 1900) : Bacteri ology ( Edinburgh, IS99) ; Eltigge, Die 11 ikro organimen (Leipzig, 1S96). See BACTERIA; MICROSCOPY ; MALARIA.