152 BACTERIA OF DISEASE 



of the soil and prevent the burying of the earth under the annual 

 fall of vegetation. 



Another class of bacteria, in common with some fungi, live 

 upon sugars and other carbohydrates, causing a decomposition 

 known as fermentation. Vinegar is due to the decomposition 

 of the alcohol in cider and other weak alcoholic solution by 

 numerous species of bacteria which appear as slimy masses and 

 are popularly known as mother of vinegar. Milk sours and co- 

 agulates through the agency of bacteria which reduce the sugar 

 to lactic acid, which in turn coagulates casein. So also 

 butyric acid, necessary in the manufacture of cheese, is produced 

 by bacteria. It will be seen from this that the products of de- 

 composition are not necessarily harmful. It is interesting to 

 note that some of the flavors of cheese and of high grade butter 

 are due to the products of decomposition and the excretions from 

 bacteria. It is evident that this might be true in the case of 

 limburger cheese and rancid butter but also remember that species 

 of bacteria are cultivated and used to impart certain flavors to 

 cheese and also to a less extent to butter. It is altogether 

 probable that this will become a common practice in our dairies. 

 Some bacteria bring about decomposition and produce secretions 

 that are exceedingly poisonous. The ptomaines found in fish, 

 cheese, ice cream, etc., are due to this cause. 



(e) Bacteria of Disease. — In contrast to the kinds of bacteria 

 mentioned above there is another group that live as parasites 

 on plants and animals producing disease either by destroying the 

 tissue and sapping the vitality or by the production of poisonous 

 compounds, toxins. Among the more terrible of these infec- 

 tious bacteria may be mentioned those producing consumption. 

 These affect especially the lungs of animals and cause, according 

 to data now available, from 150 to 200 thousand deaths annually 

 in the United States. It is altogether probable with complete 

 returns that the death rate will exceed by 50 thousand the higher 

 figure mentioned above. Consumption is no longer considered 

 so fatal a disease as formerly. A person of ordinary constitution, 

 if suitably nourished, can be cured by living in the open air. 

 This pest could probably be wiped out within ten years, if the 



