INTRODUCTORY HISTORICAL REVIEW 19 



access by the air the development of microorganisms would not take 

 place. It was then claimed by the adherents of the theory of spon- 

 taneous generation that the expulsion of the air by boiling and the 

 arrangements which prevented it from reentering also prevented 

 spontaneous generation. Franz Schulze and Theodor Schwan then 

 devised methods to permit air to enter after it had either passed 

 through sulphuric acid or had been heated in a glass tube. Schwan 

 also showed that when certain poisonous chemicals were added to 

 the meat infusion, microorganisms were not developed. His experi- 

 ments were the first to show the effects of what we now call anti- 

 septics^ upon microorganisms. Schroeder and Dusch allowed air to 

 enter the vessels containing boiled organic substances through glass 

 tubes which had been plugged with cotton. This method is now 

 universally used in bacteriologic work to protect sterile culture media 



FIG. 3 



Pasteur bulb. 



or pure cultures from contamination. The experiments of the last 

 two investigators were, however, not all successful, and development 

 sometimes occurred in their cotton-plugged glass vessels. The 

 question of spontaneous generation was not definitely settled when 

 Pasteur took it up before 1860. He showed, in the first place, that 

 a short boiling of an infusion of organic material was not sufficient 

 to kill all microorganisms, and that some could evidently withstand 

 the temperature of boiling water for several hours. It was subse- 

 quently shown by the botanist F. Cohn and by Robert Koch that 

 these resistant forms of microorganisms were the spores of bacteria. 



1 The term antiseptic in its strict sense means something which will prevent putrefaction 

 or sepsis by inhibiting the growth of microorganisms, while the term germicide designates 

 something that will kill germs or microbes. The word disinfectant is used synonymously with 

 germicide. In practice most substances which act as antiseptics in a certain concentration 

 will generally in a stronger concentration act as disinfectants or germicides. The term anti- 

 septics, disinfectants, and germicides are used quite indiscriminately, and there is, indeed, 

 between them no real generic difference but only one of degree. 



