58 VETERINARY rATIIOLOGY. 



soil bacteria and many water bacteria appear to live and thrive 

 on simple inorganic substances. In fact most bacteria are capable 

 of adapting- themselves to an inorganic food medium. Food sub- 

 stances must be in a dilute form in order that bacteria may 

 subsist upon them. This is probably because of the osmotic 

 differences of bacteria and their surroundings. Some 

 chemic substances, usually considered as destructive to 

 bacteria, when sufficiently dilute are food for some organisms, 

 thus the Liacillus I^antotropus produces formalin and then uses 

 it for food. It is said that BacillusPantotropus may live and 

 thrive in a 1 to 15,000 solution of formalin. Bacteria as a rule 

 require food media of neutral or slightly alkaline reaction, (as 

 shown by litmus paper) though some grow readily in acid media. 

 While foods are required in small quantities only for each 

 bacterium, yet because of their rapid mutiplication and the 

 resulting enormous numbers, the (piantity of food substances 

 consumed 1)v them becomes of considerable importance. 



Most foods of bacteria like those of animals or higher plants, 

 must undergo modification preparator}- to assimilation. As 

 previoush- stated, bacteria do not possess a digestive tube 

 neither do thev have the power of enveloping particles of food 

 as do some protozoa. Bacterial digestion is an extracellular 

 process, i. e., the bacterium digests food substances that are 

 putside of its own Ijodv. This process is the same as the 

 digestion in higher animals, the digestive tube in the latter 

 being outside of the body tissues. Bacterial digestion is the 

 result of activity of ferments produced by the body protoplasm 

 and in this respect is comparable with equine digestion Avhich 

 is the result of activity of ferments produced by protoplasm 

 of the salivary, gastric, pancreatic cells, etc. Some bacterial 

 digestive ferments are ver\- similar if not identical to the 

 digestive ferments of higher animals. 



Digested foods or food substances in solution pass into the 

 bacterial body by osmosis. 



Bacterial respiration is a simple process. The exchange of 

 gas is probably accomplished by means of the transfusion of 

 fluids containing the respiratory gas. Bacteria may vary in their 

 oxygen re(|uirenicnt. Aerobic bacteria are those that require 

 oxygen as a respiratory gas. Some bacteria will not develop 

 in the absence nf free ogygen, ol)Iigatory aerobes. Although 

 it was originally supposed that all forms of life required free 

 oxygen this is now knowm to be an erroneous idea. Thus, the 

 anaerobic bacteria require the absence of free oxygen ; and some 

 organisms, — obligatory anaerobes — ^require the absolute absence 



