200 



MODERN HORSE MANAGEMENT 



[chap. 



taining poisonous microbes) is far more danger- 

 ous than septic water, as milk contains minute 

 globules of fat. 



Microbes may reach the air sacs of the lungs. 

 Here they have very little difficulty in passing 

 into the circulation by the lung capillaries. In 

 the same way they may pass through any 

 mucous membrane, which may be reached by 

 way of the genital organs, the navel, the eye, 

 etc. Skin, as long as it is healthy, will not 

 admit the passage of bacteria, but directly it 

 becomes cut, bruised or burned the reverse is 

 the case. 



From the above remarks the reader may 

 wonder how it is that every animal and person 

 has not always some disease, there being no 

 doubt that we are in constant contact with 

 millions of pathogenic organisms almost every 

 day of our life. 



786. How the System Fights Against Microbes 

 that Produce Disease. — Firstly, many portions of 

 the body prevent the entrance of microbes. 

 Unbroken or undamaged skin is an impossible 

 barrier. Lymph is an antiseptic. The sub- 

 cutaneous tissues prevent admission, partly 

 mechanically, by forming fresh tissue. Mucus, 

 which is present on the mucous membrane of 

 the respiratory tract, etc., is an antiseptic. The 

 mucus, by continually moving, prevents a per- 

 manent lodgment. Perspiration is a slight anti- 

 septic ; the conjunctiva of the eye is protected 

 by irrigation ; the lachrymal secretion (tears) is 

 slightly antiseptic, eyelashes and eyebrows and 

 hairs in the nostrils also assist. The tiny hair- 

 like cilia in the nasal passages and windpipe are 

 continually waving towards the nose and mouth 

 respectively, the cilia in the womb are continu- 

 ally waving towards the exit ; saliva is slightly 

 antiseptic (although a healthy human mouth 

 may have as many as fifty kinds of bacteria in 

 it at the same time). Air, as it enters the lungs, 

 is filtered from bacteria by the cilia and wet 

 mucous membrane of the nasal passages ; hence 

 the necessity for always breathing through the 

 nose. 



Bacteria which pass through these traps are 

 probably caught before they reach the minute 

 air sacs of the lungs. The gastric juices in the 

 stomach are antiseptic. Nervousness affects the 

 supply of these juices very considerably, and 

 thus nervous people often pick up diseases 

 through nervousness. Bile is slightly antiseptic. 

 The juices in the intestines, however, are very 

 slightly, if at all, antiseptic ; in fact, the number 

 of bacteria in the intestines increases from the 

 stomach to the end of the large intestine (colon). 

 If the tissue is quite healthy, the presence of 

 these microbes does no harm ; thus pus-produc- 

 ing streptococci and other germs are always 

 present in large numbers, and typhoid bacilli 

 may be present in large numbers without ever 

 affecting the system. 



The case of a cook in New York City having 

 been in the best of health, but having had 

 typhoid bacilli inside her in large quantities for 

 two years, is one instance of such possibilities. 

 This woman, on account of her being unclean 

 in her habits, caused about 200 cases of typhoid 

 fever and twenty deaths before anyone suspected 

 that she was the cause. 



Thus it must be clearly understood what an 

 important part good health plays in the pre- 

 vention of germ disease. 



787. After the germ has reached the system, 

 i.e. the blood circulation, it meets with two most 

 important enemies : the one, the white blood 

 corpuscle ; the other, chemical poisons (poisons 

 that either kill the microbe or else chemically 

 destroy the toxin produced by the microbe). 

 White blood corpuscles (leucocytes) are, strictly 

 speaking, the scavengers of the body, and are, 

 therefore, called phagocytes. Their chief func- 

 tion is to devour foreign bodies, such as bacteria. 

 Then, again, the system contains certain anti- 

 toxin poisons that destroy certain bacteria, or 

 destroy toxins produced by bacteria. Thus one 

 animal would possess one antitoxin and another 

 would possess another, and, therefore, one 

 animal might be immune or safe from contagion 

 to one disease, whilst another animal might 

 contract it. 



788. Immunity from Disease. — Immunity can 

 be natural or acquired. As stated above, certain 

 animals and certain races are naturally immune 

 against certain diseases ; thus vertebrates are 

 generally immune against invertebrate diseases, 

 and cold-blooded animals immune against warm- 

 blooded animal diseases. Individuals also 

 possess striking immunity from certain diseases. 



Acquired immunity is of two kinds : active 

 and passive. Active immunity is due to direct 

 participation of the microbe concerned ; for 

 example, the inoculation, by means of vaccina- 

 tion, of the microbe of cowpox, which produces 

 a mild form of smallpox. 



Passive immunity, on the other hand, necessi- 

 tates no active generation of the disease in 

 question, but consists in introducing chemicals 

 (antitoxins) into the system that make that 

 system immune against that particular disease. 

 For example, diphtheria is prevented by the 

 introduction of diphtheria antitoxin ; lockjaw, 

 by the introduction of antitetanic toxin. Passive 

 immunity, however, is not so permanent as 

 active immunity, and in most cases disappears 

 rapidly. 



789. Active immunity may be produced in 

 the following ways : 



1. By introducing living bacteria of full viru- 

 lence in a small quantity, which is gradually 

 increased. The disease is thus produced in a 

 mild form, which apparently produces anti- 

 toxins and makes the subject immune after- 

 wards. 



