92 ACTIVITIES OF BACTERIA. 



Also higher alcohols: Glycerin, dulcite, and mannite are 

 changed into acids; glycerin as constantly as sugar is 

 (v. Sommaruga, Z. H. xv, 291). 



Finally, numerous results have been obtained regarding 

 the transformation of acids of the fatty series (or their 

 salts) into other fatty acids by bacteria. Unfortunately, 

 the earlier observations were made without the employ- 

 ment of such pure cultures as satisfy the present demands. 

 Usually lactate, malate, tartrate, citrate, and glycerate 

 of calcium were employed, while almost always mixtures 

 of acids were obtained as a result of the activity of the 

 bacteria. Among these, butyric, propionic, valerianic, 

 and acetic acid play the principal rdle; often also there 

 occur succinic acid, ethyl alcohol, and more rarely formic 

 acid. Of gases, carbonic acid and hydrogen occur 

 especially. 



Such investigations -were formerly carried out particularly by Fitz, 

 and more recently they have been performed on an extensive scale 

 "vvith undoubtedly pure cultures and with interesting results by 

 P. Frankland. 



Here only two illustrations are given: Pasteur found that anaerobic 

 bacteria converted lactate of calcium into the butyrate: 



2(CH3 — CHOH — C00)2Ca = 



Lactate of calcium. 



COaCa + 3CO2 + 4Hj + (CH3 — CHj, — CH^ — COO)Ca 

 Butyrate of calcium. 



Accoi-ding to P. Frankland, the Bacillus sethaceticus Fitz forms from 

 the glycerate of calcium, (CHjOH-CHOH-C'OOjzCa, ethyl alcohol, 

 acetic acid, carbonic acid, and hydrogen. 



5, THE PATHOGENIC ACTION OF BACTERIA 



(PATHOGENESIS, PREDISPOSITION, 



RESISTANCE, IMMUNITY). 



I. How Do Bacteria Act Pathogenically ? 



If micro-organisms enter the tissues or blood of an 

 animal, there occurs an infection if, at the same time — 



1. The micro-organisms can remain alive and increase 

 within the host. 



2. If the micro-organisms produce substances which are 

 injurious to the host. 



