152 PHYSIOLOGY OF MICROORGANISMS 



Unicellular organisms are concerned with what may be called 

 respiration. Oxygen, in its free forms, is needed in most instances for 

 body-processes and carbon dioxide is given out. The amount required 

 varies with different organisms and is not determined by the amount 

 present in the air. Other gases are also used. Nitrogen is taken up 

 by the microorganisms which grow on the roots of legumes; marsh-gas, 

 carbon monoxide, carbon dioxide, hydrogen and other gases are claimed 

 to be utilized. Each species of microorganisms seems to possess greater 

 or less specificity in its gas-relations. No species can extend its influ- 

 ence over all amounts of a single gas or to all gases. From this situation 

 it is a forced conclusion that all cells do not function alike, accordingly 

 must have different mechanisms although the capacity for life appears 

 common to all. 



Some organisms emit light or manifest radiant energy, other organ- 

 isms produce pigments which vary with different species, still others 

 elaborate deadly poisons, called toxins, and other substances of patholog- 

 ical significance. Briefly, microorganisms give rise to many different 

 products whether they take the form of secretions, excretions, energy 

 manifestations, or are referable to action upon environmental media. 

 Enumeration is not the purpose here. These very numerous products 

 indicate the many-sided activities of microbial life. If the substances 

 which enter a mechanical device are the same, the products passing out 

 are the same. In this case, the food substances and the conditions 

 controlling the microorganisms may be identical yet the issuing products 

 are different. It follows, therefore, that the mechanism of cells must 

 be very different, yet as mentioned heretofore the life-mechanism is 

 common and the same so far as determinable. 



Many unicellular forms have a cell-wall and when no cell-wall is 

 present there is likely to be a distinctive and denser layer of cytoplasm 

 on the outer zone. Some organisms when placed in a dense salt 

 solution will lose a considerable amount of their water-content and 

 shrink while others will not; in other words, some microorganisms have 

 the power of withstanding dense brine while others do not. Osterhout 

 has repeatedly demonstrated that where two salts are together in a 

 medium acting as a substratum for microorganisms there may exist 

 an antagonistic or favorable action of one of the salts upon the absorp- 

 tion of the other salt by the cell but that cells vary in these responses. 



It is a common knowledge that cells have a selective action which 



