August 1, 1889.] 



♦ KNOV^LEDGE ♦ 



205 



as to allow the mucus secreted by the glands to be gradu- 

 ally moved upwards. When bacteria and other particles 

 are inhaled they are drawn down into the larger bronchi by 

 the inspiratory effort, and come in contact with the lining 

 epithelium with its covering of sticky mucus ; to this they 

 adhere and are lashed up by the cilia to be expectorated. 

 The terminal air vesicles and passages, where the exchange 

 of gases between the blood and the atmosphere chiefly takes 

 place, have a lining of only a single layer of flattened cells. 

 Two circumstances protect these : firstly, in ordinary respira- 

 tion the air is not drawn down to these cells with any force, 

 it merely diffuses into them, and the bacteria probably 

 would have been caught by the mucus above ; secondly, tlie 

 nervous mechanism here is readily stimulated by an irritat- 

 ing particle such as a tubercle bacillus, and the result is a 

 forced emptying of the passage by a cough, which drives 

 upwards the irritant. When by any chance the healthy 

 continuity of the epithelium is broken and the entrance of 

 bacteria allowed, there is still a battle to be fought. If the 

 injury has not seriously lowered the vitality of the tissues, 

 most bacteria will have but a poor chance of life. There 

 are the scavengers already referred to ; normally their vitality 

 exceeds that of the bacteria they devour. The chemical 

 processes occurring everywhere in our bodies also do much 

 to destroy bacteria. Possibly also the rapidity of the blood- 

 stream may have something to do with their destruction ; 

 we know that active motion is antagonistic to their life outside 

 the body, and therefore the same influence may act within. 



It is of course possible for an army, if suSiciently 

 numerous, to overcome defences, however complete they 

 may be. The admirable natural defences of the healthy 

 living body can be thus broken down by abnormally great 

 numbers of bacteria. In Koch's experiments on the 

 tubercle bacillus, he showed that the inhalation of them in 

 gi'eat numbers by healthy guinea pigs readily caused tuber- 

 culosis; the injection of them into the blood pi'oduced 

 the same result. Another striking example is the case of 

 the micrococci of suppuration ; if we apply a poultice of these 

 to the human skin a boil results. In nature, however, we 

 are practically never exposed to such extreme conditions. 

 There are also certain bacteria whose virulence is so great, 

 that probably but few of us could resist them when once 

 introduced into the system. Such is the ease with the 

 bacillus that causes that fatal disease of cattle called anthrax, 

 and which often causes a similar disease in men, especially 

 among farriers and wool sorters. 



We now come to the consideration of the second method 

 of defence, viz., how to destroy and disable the foe. An 

 important way of getting rid of our bacterial foes is to cut 

 ofl" their supplies, destroy their habitations and means of 

 locomotion. In towns the proper attention to sanitary 

 arrangements, the proper disposal of the drainage, the 

 efficiency of the water supply, the cleanliness of the streets, 

 houses, and people are some of the principal modes in which 

 this part of the warfare can be carried on. The avoidance 

 of dust is also important. It has already been stated that 

 the bacteria in the air are principally carried by particles 

 of dust ; but another reason is that the continual in- 

 halation of many particles of dust by itself causes irritation 

 to the lungs, and is apt to produce chronic inflammatory 

 mischief, the results of which give opportunities for the 

 entrance of bacteria. Thus in many trades, such as needle- 

 grinding and .stone-cutting, the proportion of deaths from 

 consumption is terribly greiit. 



The direct destruction of bacteria by implements of war 

 is also demanded. The principal implements we use are 

 poisons and heat. These we term disinfectants and anti- 

 septics. The disinfectants are those which directly kill 

 the organisms and their spores, the antiseptics those that 



hinder their development and stop their spore formation. 

 Important poisons are corrosive sublimate, carbolic acid, 

 arsenic, chlorine, and many others. Their relative value 

 cannot be discussed here ; in fact, it is a subject much dis- 

 puted. By these agents we can destroy the bacteria where 

 they are known to exist to a dangerous degree, such as in 

 fever chambers, mortuaries, drains, &c. Their use in 

 epidemics is evident. 



Heat is a disinfectant, and, moreover, it is one of the most 

 important we have. Dry heat is less powerful than moist 

 heat : in using it the temperature of over 284° Fahr. must 

 be prolonged for some time to make sure of killing both 

 the organisms and their spores, while steam at 212° i-apidly 

 kills ail bacteria. Heat is greatly used to disinfect clothing, 

 &c., and the heat used in cookery is an important agent in 

 times of epidemic, especially of diseases aflecting the alimen- 

 tary tract, such as typhoid and cholera. In these cases the 

 boiling of water and of milk is very important. In refer- 

 ence to tubercvilosis, the boiling of milk is a matter of very 

 serious importance, especially in towns where cows are kept 

 in stables for dairy purposes. Cows under such unnatural 

 conditions are very apt to become tubercular, and unfortu- 

 nately when aSfected they may show but little or no external 

 evidence of the disease. The milk of tubercular cows very 

 frequently contains a great abundance of tubercle bacilli ; 

 hence the danger. Epidemics of scai'let fever have also been 

 traced to the use of unboiled milk. 



It is a common practice in warfare to make our enemies 

 destroy each other. We can sometimes do this with 

 the foe under consideration. Some bacteria thrive on 

 certain soils much better than others ; these will outgrow 

 and starve out the less favoured. In some cases such 

 antagonistic actions can take place in the body. For 

 example, there is an antagonistic action between the anthrax 

 bacillus and erysipelas micrococcus. If we take two animals 

 susceptible to anthrax disease, and inoculate them both with 

 the bacillus, then a short time afterwards inoculate one of 

 them with erysipelas virus, the result is that the one 

 which has simply had the anthrax inoculated dies, the 

 other lives. It is one of the gre.vt aims of modern medical 

 investigations to try and cure grave diseases by giving the 

 patient another of a comparatively trivial and curable 

 character. In connection with this we recognise the friendly 

 actions of some bacteria, which, although unpleasantly 

 stimulating our olfoctor}' apparatus by their volatile secre- 

 tions, do us great service in choking out others that might 

 be a source of serious danger. 



There are many bacterial diseases of which one attack, 

 even though of the most trivial character, protects the 

 patient from a future attack. The reason of this is at 

 present a mystery. From this it is evident that, if we Ciin 

 disable the power of bacteria, so that a slight attack may be 

 given, a great advantage is obtained. This has been done 

 in several ways — b)- giving the disease to a different animal, 

 and collecting the virus from it ; by cultivating the 

 organisms in some non living medium for many geuei-ations, 

 or by cultivating thorn under some peculiar conditions, such 

 as excessive heat. The earliest and by far the greatest 

 good done for mankind in this way was through the 

 researches and brilliant discovery of vat'ciuation by Edward 

 Jenner many years before such things as bacteria were even 

 heard of. He discovered that smallpox, after having 

 passed through the cow, was converted into a disejise so 

 simple as to cause only the trivial results of proper vaccina- 

 tion. Vaccination does not give complete immunity from 

 smallpox, but mitigates its character ; by it one of the most 

 horrible of diseases, malignant smallpox, has practically 

 ceased to exist, and in its place we find a comparatively 

 trivial disease, i.e. the smallpox of the present day. 



