CHAPTER XVII 



BACTERIOLOGY, ANTISEPTICS AND THE THEORY OF DISEASE 



769. Theory and Prevention of Disease. Disease 

 (literally, without ease) is defined as " an 

 abnormal condition of a vital tissue." A diseased 

 condition, however, must not be confounded 

 with an abnormal condition of an organ com- 

 posed of healthy tissue, such as a corn, which 

 is merely a hypertrophy, due to irritation, or an 

 enlarged muscle, which is due to excessive 

 nourishment being supplied to the part, a result 

 of increased exercise to the part. The tissue 

 itself, and not only the organ, must be actually 

 abnormal, otherwise there is no disease. Disease 

 is caused in two ways : firstly, by a micro- 

 organism, in which case the disease is said to 

 be contagious or infectious ; and, secondly, by 

 other means than such organisms. 



770. We will consider the second condition 

 first, as it does not concern us so much in this 

 chapter. Diseases produced by non-contagion are 

 those produced by a breakdown in tissue, due 

 to excessive strains, by a breakdown in the 

 nerves supplying the parts, by arrest of blood 

 supply to the part, and by abuse of habits, such 

 as use of liquor, smoking, etc. Diseases pro- 

 duced in this way are paralysis, heart disease, 

 diabetes, liver disease, various nervous diseases, 

 etc. 



The prevention of such diseases is clearly the 

 removal of the cause, healthy living, plenty of 

 good exercise to all parts of the body, absence of 

 worry, faith in one's own health. The cure is 

 healthy exercise, fresh air, moderate habits, care- 

 ful dieting, absence of worry, and faith in one's 

 own health. I deal with the prevention of 

 human disease at the end of this chapter. 



771. Contagious Diseases. Diseases produced 

 by contagion are those that are receiving the 

 greatest consideration to-day. We will consider 

 how such are produced, how they are spread, 

 how they are prevented, and how they can be 

 cured. 



Micro-organisms are of two kinds, animal 

 and vegetable. The former are called protozoa 

 (one cell), the latter, bacteria, yeasts, and moulds 

 or fungi. 



The surface of the earth and everything on it, 

 as well as the atmosphere, is covered or filled 

 with millions of vegetable micro-organisms. In 

 fact it would be impossible for life to continue 



without these germs. These vegetables are in 

 reality our best friends, and it is only by accident 

 that a small percentage (not more than 2 per 

 cent.) do us any harm. 



Bacteria and yeasts carry out one of the most 

 important functions that exists in the world. All 

 putrefaction and decay are due to bacteria. Bac- 

 teria destroy dead bodies, and transform import- 

 ant chemical elements like nitrogen and carbon 

 from unavailable combinations into substances 

 that can be utilised and changed into higher 

 forms of plant life. Bacteria modify the compo- 

 sition of the soil and the character of crops, and 

 are, therefore, of the greatest use to farmers ; 

 bacteria impart the flavours and the aromas to 

 butter, cheese, milk, etc. ; bacteria are respon- 

 sible for the tanning of hides, retting of flax, 

 and the curing of tobacco. 



Vinegar, which is acetic acid, is formed by 

 bacteria. The chemical equation is as follows : 

 C 2 H 5 (OH) (alcohol) + 2 (oxygen) = HC 2 H 3 0, 

 (acetic acid) + H 2 (water). 



Lactic acid bacteria eat and digest the acid 

 and make cheese. 



Formerly, ammonia was made by the action 

 of bacteria on urine, forming ammonium car- 

 bonate. 



Iron is liberated as iron hydrate in some bogs 

 by bacteria. 



The acidity of peptone, an agent in the diges- 

 tive system, is due to bacteria. 



Gelatine is produced partly by the action of 

 bacteria. 



The preservation of many foods is due to 

 bacteria. 



772. Fermentation is due to yeast cells, which 

 break up the structures that they attack in order 

 to obtain nourishment for themselves, and in 

 doing this they cause important chemical 

 changes to take place. For instance, yeast cells 

 are present on the outside of all grapes, and 

 when grapes are put into a vat for the purpose 

 of making wine, the yeast cells cause fermenta- 

 tion ; if these cells were not present, fermenta- 

 tion would not take place. The yeasts convert 

 all starches into sugar by combining a molecule 

 of starch with a molecule of water and forming 

 grape sugar (glucose or dextrose) : C 6 H 10 5 + 

 H,0 = CeH^O*. 



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