192 Theobald Smith 



class belong the greater number of the gas-producing bacteria 

 to be considered farther on. It corresponds to the facultative 

 anaerobic group, that is, those forms which are capable of 

 multiplying to a certain extent in media free from oxygen al- 

 though they flourish best in the presence of this gas. 



There is lastly a third group of bacteria, of which I have 

 examined only a small number in the course of the past four 

 or five years, which do not multiply in the open bulb but seek 

 the closed branch. These are the strictly anaerobic forrus 

 which require a medium devoid of oxygen. Many of them 

 are gas-producing. 



The fermentation tube thus informs us at once to which of 

 these three groups of bacteria any given species belongs. 

 This determination is especially valuable with the facultative 

 anaerobic and the aerobic species. The anaerobic nature of 

 any given form is usually manifested beforehand by its refusal 

 to multiply in the ordinary culture tubes. It is needless for 

 me to go over the various methods and devices which have 

 been and are still employed in defining the aerobic or anae- 

 robic character of bacteria. They are given in part in current 

 text books. The simplicity of the test in the fermentation 

 tube will at once appeal to all who have striven to produce a 

 vacuum or substitute for the air an atmosphere of hydrogen. 



The possibility of cultivating aerobic and anaerobic bacteria 

 in the same kind of tube makes more simple certain bacterio- 

 logical work carried on hitherto under considerable difficulty 

 and with but partial success. In the determination, both 

 quantitative and qualitative, of bacteria in the soil or the in- 

 testinal tract for instance, the aerobes and anaerobes had to 

 be dealt with separately. In the solution of such problems 

 the fermentation tube may do good ser\'ice if the method of 

 dilution be employed. Since this tube shows no discrimina- 

 tion between these two physiological groups of bacteria all 

 would have an opportunity to develop. I am well aware of 

 the difficulties inherent in the method of dilution, — the diffi- 

 culty of gauging the dilution beforehand, the large number 

 of tubes required, the care to be taken in the manipulation of 

 the fermentation tubes, their size and cost — but these diffi- 



