GLOSSARY 283 



16. Because most of the elements form analyzable 

 compounds with oxygen and few with hydrogen, 

 oxygen =16 was adopted as the more convenient 

 standard. (Taking 16.00 as the atomic weight of 

 oxygen, it was later found that the atomic weight 

 of hydrogen is 1.008.) 



Autolysis. The disintegration of tissues caused 

 by the action of their own ferments. 



Avogadro's Constant. The number of molecules 

 in a gram-molecule. (Symbol A^.) iV =6.062 xlO^^, 

 It is the famous rule of Avogadro (stated in 1811) 

 that given the same temperature and pressure, 

 equal volumes of all gases contain equal numbers 

 of molecules. 



Bacteria. Microorganisms. Bacteria were first 

 discovered by the Dutch naturalist Anton van 

 Leeuwenhoek in the last quarter of the seventeenth 

 century. About a hundred years later the Danish 

 investigator Miiller made further observations. In 

 1838 Ehrenberg, who discovered iron bacteria, de- 

 scribed a large number of bacteria. The study of 

 bacteria now ranks among the most important sub- 

 jects of research from several approaches. The re- 

 sults which crowned the experiments of the pathologists 

 Robert Koch, Pasteur, and Metchnikoff, have made 

 the widest possible appeal. Special interest also 

 has centered in the nitrifying bacteria, which became 

 known chiefly through the investigations of S. 

 Winogradsky, Many hundreds of different bacteria 

 are known and described. Bacteria are found in the 

 alimentary canal of animals, and distributed in the air 

 and in water, etc. Those that are injurious to the 

 health of animals and plants are termed pathogenic. 

 Most infectious diseases are due to bacteria; as 

 diphtheria, to the bacillus of diptheria; typhoid 

 fever, to the bacillus of typhoid fever, etc. Some 



