BACTERIA. 159 



For the Chemical Composition of Bacteria, we are indebted to 

 Nencki. Their constituents vary slightly according as to whether 

 the bacteria are in zoogloea, or in the active state. In loo parts 

 of the dried constituents, there are the following : — 



A nitrogenous body 84-20, Fat 6-04, Ash 472, undetermined 

 substances 5*04. This nitrogenous body is Mycoprotein, so-called, 

 and consists of Carbon 52-32, Hydrogen 7-55, Nitrogen 14-75, 

 but no sulphur or phosphorus. The nitrogenous body appears to 

 vary with the species, for ^in Bacillus anthracis a substance has 

 been obtained which does not give the reactions of mycoprotein, 

 and, therefore, is distinguished as anthrax-protein. Bacteria can 

 and do utilise the last traces of energy in urea. It is the Bacteria 

 which play the most important part in disease, exciting both 

 general and systemic affections. The others — e.g.^ Blastoniycetes 

 (yeasts), and Hyphomycetes (moulds)-exert a merely local influence. 

 The animal parasites become dangerous in virtue of their size, or 

 multitude, or by penetrating into vital organs. Special reagents or 

 staining processes have to be employed to discover them ; some- 

 times certainty is only reached by experimental cultivation of the 

 products of disintegration of the tissue in question. 



Reagents. — Water is essential for their growth, though depri- 

 vation does not kill all the bacteria. Different species grow best 

 on different nutrient media. 



Effect of Temperature. — Here again they vary, many grow best 

 at the temperature of the blood, and hence the value of agar-agar 

 media, which is not liquefied at 37^^ C. (or 98-60 F.) The 

 B. tuberculosis will only grow at a temperature varying between 

 30° C. (= 86 F.) and 41^ C. (= 109° F.). 



Cold. — The Bacteria seem to have a special power of resisting 

 cold; even comma bacilli, if exposed to a temperature of — lo*^ 

 for an hour, and bacilli of anthrax after exposure to a temperature 

 — 110° C, still retain their vitality. The spores retain their 

 vitality after immersion in boiling water, but are destroyed by 

 prolonged boiling. 



Movement prevents their growth. 



