SYMBIONTICISM AND ORIGIN OF SPECIES 105 



summaries and data which may be found in text-books 

 and monographic works on bacteriology, however, contain 

 many examples of known bacterial activity which form 

 valuable evidence for our purpose. It has been claimed 

 that there are no enzymatic properties in the human body 

 that are not also represented in bacteria (Jordan, '24). 

 It may not be possible to completely verify this state- 

 ment. Evidence that supports this however is abundant. 

 In Marshall's "Microbiology" ('21) considerable attention 

 is given to the metabolic products of microorganisms. 

 After a perusal of this book, it is evident that bacteria 

 produce metabolic products that are identical in their 

 properties with those elaborated by plant and animal 

 cells. A brief summary of some of these activities may 

 serve to illustrate this point. 



The better known enzymes of animals and plants are 

 concerned with food digestion. While we do not know the 

 chemical composition or structure of any of these enzymes, 

 their chemistry is known in terms of the reactions they 

 produce with carbohydrates, fats, and proteins. These 

 enzymes are known to be the products of various glands 

 collectively known as "digestive glands" in the higher 

 animals. Some of them are also present in plants. The 

 enzyme concerned with starch decomposition — amylase 

 (ptyalin, diastase) — is a particular product of the salivary 

 glands, and also of the pancreas. Amylase hydrolyzes 

 starch and changes it into maltose, a sugar. Regarding 

 the occurrence of amylase in nature, Marshall states: 

 "Diastase, or amylase is a starch-dissolving enzyme which 

 is one of the most common enzymes in nature. It is found 

 in all green plants, and it forms during the sprouting of 

 starchy seeds. Many moulds and a few bacteria produce 

 this enzyme, while yeasts generally cannot decompose 

 starch for lack of diastase." Cellulose is closely related to 

 starch, and is decomposed into a soluble sugar by an enzyme 



