188 



KNOWLEDGE. 



[August, 1901. 



poiut, with the object of breeding pure cultures of the 

 races to which a good cigar may owe its peculiarly 

 seductive aroma. 



These are a few only of the almost numberless cases 

 iu which we are indebted not only for our luxuries but 

 for the very means of life itself, to the silent but ceaseless 

 labours of these tiny organisms. Moreover, if there is 

 anything whatever in the theory of modification by 

 descent, we ought to be able — considering their fabulous 

 rate of multiplication — to bring about in a comparatively 

 short time changes in the structure and habits of some 

 of our " tajue " bacteria which will make them minister 

 to our health and comfoi-t to a degi-ee hitherto un- 

 dreamt of. 



Whilst, however, we freely admit our great indebted- 

 ness to bacteria, we must not forget that their powers for 

 evil are also enormous. 



In 1849, Pollender discovcied minute rod-like bodies, 

 one four-thousandth of an inch long, in the blood of 

 animals which had died of anthrax or splenic fever, and he 

 suggested that these tiny rods bore some definite relation 

 to the disease.* Fourteen years later Davaine announced 

 that the rods were living plants, and that blood contain- 

 ing them had the power of passing on the disease to 

 another animal inoculated with it; while blood from 

 which the bacilli were absent had no power of confer- 

 ring the disease. About 1876 Koch discovered how to 

 grow the organism outside the body ; and Pasteur sub- 

 sequently found that by keeping artificial cultures of the 

 anthrax bacillus at a temperature slightly above that 

 of the blood the organisms gradually lost their deadly 

 power, and after 43 days had no injiu-ious effects upon 

 even the most susceptible animals. After being inocu- 

 lated with such harmless cultures, the animals were sul> 

 jected to the action of cultures of gi-adually increasing 

 strength, until after a short time it was found that they 

 could easily withstand a dose which would at first have 

 proved immediately fatal. The animals had. iu fact, 

 become protected against the disease. This brilliant dis- 

 covery has already been put to very extensive use, and 

 the method of inoculation is now recognised as a certain 

 means of protecting horses, sheep, cattle, and even ele- 

 phants against the ravages of splenic fever. 



The activities of the anthrax bacillus may be regarded 

 as illustrating the ways of malignant bacteria generally. 

 There is, however, considerable variation in minor details 

 of structure and mode of life. For example, while the 

 rod-shape or bacillus is the form of the organisms respon- 

 sible for anthrax, typhoid, diphtheria, " consumption," 

 and some other diseases, the microbes giving rise to 

 erysipelas are not bacOli, but minute globular bodies 

 (cocci) which stick together in rows, like beads ; and 

 the cause of cholera is a tiny comma^shaped bacterium. 

 While, again, some microbes gain access to the blood, 

 and thus by their marvellous powers of multiplication 

 spread throughout the whole body, others remain at the 

 point of inoculation, and yet set up profound distiu-bances 

 in the system generally which ultimately end in death. 



The last-mentioned fact, that the organisms themselves 

 may be restricted to one point, while their evil effects 

 may extend throughout the body, suggests that during 

 their life they give off poisonous substances to which, 

 rather than to the bacteria themselves, the diseases are 

 due. This has repeatedly been proved to be the case. 

 , Here, again, anthrax furnishes an instructive example. 

 It has been found possible to prepare from artificial 

 cultures of the anthrax bacillus an intensely poisonous 

 substance, which is nevertheless free from the bacteria ; 



and this poison or toxin of anthrax induces, if injected 

 into the blood of an animal, all the characteristic 

 symptoms of the disease. Nor is this all. The strength 

 of the toxin can be so regulated that while it is insuffi- 

 cient to cause death, it protects the animal against future 

 attacks. 



The theoi'y which at present best explains these re- 

 markable facts is that the toxins stimulate certain cells 

 of the body to manufacture substances which neutralise 

 them. These toxin-destroying substances are called 

 nntitocins. Once the cells have got into the habit, so to 

 speak, of producing antitoxins, they continue the work, 

 and lay in a stock which is suificient to promptly render 

 useless the poison-armoury of -the particular race of 

 bacteria, should these again invade the territory. 



The fact that the terrible zymotic diseases are due to 

 blood-poisoning by toxins, and the possibility that for 

 every toxin there is a corresponding antitoxin — in other 

 words, that every disease produces its own antidote — 

 which may yet be discovered and isolated, are sufficient 

 to explain the tireless enthusiasm with which bacterio- 

 logists have of late years carried on their researches. 

 Marked success has in many cases attended their efforts, 

 and the manufacture of certain antitoxins is now carried 

 on upon a somewhat large scale. The antitoxin of 

 diphtheria, for example, is regularly prepared by a large 

 German firm, and sent out to all parts of the world. The 

 bacilli of the disease are first grown in speciallj' prepared 

 broth for about a mouth, by which time the fluid has 

 become strongly impregnated with the poisonous toxin. 

 The bacteria are filtered off, the clear solution obtained 

 containing the toxin. This is then injected into horses 

 in gradually increasing doses, until the animals can with- 

 stand a large quantity without inconvenience. Then 

 after a few days' rest they are bled from the jugular 

 vein. The whole operation is so carried out that the 

 horses suffer practicallv no pain whatever, and very little 

 injury to their general health. The blood is allowed to 

 clot, and the clear fluid (serum) which rises to the top 

 contains the antitoxin, and is hence known as~anti-diph- 

 theritic serum. It is now injected, iu closes varying 

 with the severity of the disease, into patients suffering 

 from diphtheria. As a result of the treatment the 

 mortality from this disease has been greatly lessened. 

 Antitoxins have also been prepared for protection against 

 and treatment of various other diseases, including 

 typhoid, tetanus (lockjaw), plague, hydrophobia, and 

 snake-poisoning. A few years ago there seemed to be 

 grounds for believing that a cure for consumption had 

 been discovered. The anticipations were, unfortunately, 

 not realised; but the extract of "tuberculin," which it 

 was hoped would rid humanity of its greatest scourge, 

 forms a means of identifying tuberculous cows, and thus 

 of removing one source of the disease. 



The indictment against these low forms of life is a 

 terrible one. Disease and dirt are, however, closely 

 connected, and the introduction of better sanitary con- 

 ditions will of necessity ext,erminate many diseases. As 

 a rule, only those in a low state of health need fear 

 these minute foes, for they are in nearly every case 

 unsuccessful against vigorous constitutions. The various 

 fluids of the healthy body have a distinctly injurious 

 effect upon malignant bacteria, and it has recently been 

 found that there are in our bodies certain wandering 

 cells which in health act as policemen, promptly seizing 

 and devouring the harmful microbes which do gain 

 access to the system. The tonsils, for example, are 

 crowded with these guardian cells. 



