186 Microbes and You 



is specific in that human streptococci can dissolve human blood 

 clots but not clots of blood from other animals. 



SPREADING FACTOR 

 Duran-Reynals reported a spreading factor which affects the 

 permeability of invaded tissues to bacteria, toxins, India ink, and 

 other substances. Some bacteria produce spreading factor and it 

 can also be found in the testes of certain animals. The invasive- 

 ness of an organism can be correlated with its ability to manu- 

 facture spreading factor. Recent studies have shown the similar- 

 it)' of this reaction to that produced with hyoluronidase, an en- 

 zyme capable of dissolving mucin-like substances. The enzyme 

 destroys hvaluronic acid, a component of the intercellular sub- 

 stance uniting body cells in tissues. 



PYROGENS 



Unless distilled water is kept free of bacteria, constituents of 

 certain organisms, even though dead, produce fever reactions, 

 called pyrogenic responses, upon injection into animals. Exact 

 chemical analyses have revealed pyrogenic fractions which are 

 carbohydrate in character, and when as little as twentv-five to fifty 

 micrograms (millionths of a gram) of this material is injected into 

 a rabbit, the animal of choice, a temperature rise of about 2.5° C. 

 will occur. Pyrogens are not uncommon in the culture medium 

 employed in the manufacture of such substances as penicillin, and 

 great care must be employed to get rid of these undesirable frac- 

 tions. The Shiga type of the dysentery organism, curiously enough, 

 produces a hypothermic (temperature-lowering) substance in its 

 metabolism. 



FERMENTATION 



This word comes from the Latin, ferveo, meaning to boil, which 

 was the most common observable characteristic of the reaction. As 

 our knowledge increased, fermentation came to signify the break- 

 down of sugar into alcohol and carbon dioxide ( Gay-Lussac's 

 work), and with the studies of Pasteur fermentation became more 



