52 PHYSIOLOGY OF NUTRITION 



§4. Distribution of Microorganisms in Nature. — The study of microorganisms 

 is possible only with the aid of the microscope, and their discovery was impos- 

 sible until magnifying glasses became available. The Columbus who discovered 

 the world of the lowest organisms, which are ordinarily invisible, was a Dutch 

 lens-maker of Delft, Anton van Leeuwenhoek. He succeeded in making mag- 

 nifying glasses that magnified 100 and even 150 diameters. When, in 1675, he 

 examined a drop of rain water that had stood for several days in a barrel, using 

 one of his glasses, he observed a vast number of extremely small organisms 

 moving hither and thither in the water. The number of these organisms ap- 

 proached 10,000 in a single drop. No such organisms were to be seen in freshly 

 collected rain water, and Leeuwenhoek therefore concluded that the germs of 

 these must have fallen into the water from the air. 



The question then arose as to the origin of these extremely small organisms, 

 and this became the subject of a very lively polemic. It is well known that 

 infusions of most organic materials, such as meat and vegetable matter, de- 

 compose very easily. Microscopical examination of material undergoing de- 

 composition always shows the presence of microorganisms. The promptness 

 with which they appear led to the conclusion that we have here a spontaneous 

 generation (generatio spontenea) of the lowest forms of life out of various 

 organic substances. 



The theory of spontaneous generation has had many adherents, even until 

 recent times. Thus, van Helmont (1 577-1644) was the author of a recipe for 

 the production of mice from meal. It was maintained that maggots (fly larvae) 

 arise by spontaneous generation in meat. Even after it had been provided by 

 exact experimentation that neither mice nor maggots can be produced de novo, 

 and that such forms must arise by propagation, still the conviction persisted 

 for a long time that the tiny, microscopic organisms may develop by spon- 

 taneous generation. As early as 1776 Spallanzani proved experimentally that 

 this theory was incorrect. He showed that no animalcules appeared in an her- 

 metically sealed vessel containing an infusion of organic material, no matter 

 how long this was allowed to stand, provided the infusion had been first boiled 

 for three-quarters of an hour. After such a vessel had been opened, however, 

 the contents soon began to putrefy; because germs entered from the air, as 

 Spallanzani maintained. Although the adherents of the theory of spontaneous 



complex carbon compounds from mineral carbonates and bicarbonates. (See Nathansohn, 

 1902, and Beijerinck, 1004. [Note 2, p. 49.]) In addition to these there are still others 

 that oxidize ferrous compounds to the ferric form. 1 See: Winogradsky, S., Ueber Eisenbak- 

 terien. Bot. Zeitg. 46: 261-270. 1888. Molisch, Hans. Die Eisenbakterien. Jena, 1 910. 

 Lieske, Rudolf, Beiträge zur Kenntnis der Physiologie von Spirophyllum ferrugineum Ellis, 

 einen typischen Eisenbakterium. Jahrb. wiss. Bot. 49: 91-127. 191 1. Idem, Untersuch- 

 ungen über die Physiologie eisenspeichernder Hyphomyceten. Ibid. 50: 328-354. 191 1. 



Since the forms, or kinds, of energy are mutually transformable it is possible that energy for 

 the syntheses that occur in organisms may be derived not only from chemical reactions and 

 light but also from other immediate sources, such as the radiant energy of heat and electri- 

 city. The heat of the medium in which the reactions occur is of course a very important 

 source of energy, not generally discussed in this connection. — Ed. 



