RESPIRATION AND OXYGEN. 97 



with decreasing CO2. Pure CO2 stopped the growth of hyphae 

 in 24 hours. Mixtures which contained 10 to 30 per cent could 

 neither suppress the growth of the hyphse nor the production of the 

 sporangia, but growth was much slower. A higher content of CO 2 

 checked growth and suppressed sporangia, but the latter developed 

 when air was substituted. Bursting of the hypha3 occurred when 

 cultures were exposed for several days to high C02-content. The 

 higher the latter, the greater the number of vacuoles in the proto- 

 plasm. The propagation of yeast was inhibited in pure CO 2, but 

 was resumed upon the replacement with air. Mycoderma cerevisice 

 was much more susceptible, and it lost its power of propagation after 

 a 12-hour exposure. 



Ortloff (1900 : 763) found that the increase of yeast-cells was re- 

 duced by a stream of CO 2, but that the amount of the fermented 

 sugar during 28-hour exposure was greater than in normal cultures. 



Chapin (1902 : 375) found that the spores of Mucor, Aspergillus, 

 and Penicillium did not germinate in a high content of CO2, but after 

 being exposed to pure CO2 for 4 months, they were able to germinate 

 when again brought into air. The amount of CO2 necessary to hin- 

 der germination was 60 per cent for Mucor and 90 per cent for Peni- 

 cillium and Aspergillus. Cessation of the growth of the hyphse took 

 place at 30 to 40 per cent for Mucor and at 80 per cent with the other 

 two. The production of spores was hindered at 20 per cent in Mucor, 

 40 per cent in Aspergillus, and 50 per cent in Penicillium. 



Kostytschew (1907 : 178) showed that the normal and anaerobic 

 respiration of Penicillium glaucum and Aspergillus niger, when nour- 

 ished with mannite, took place without the formation of hydrogen, 

 and apparently without anything in common with alcoholic fermen- 

 tation. He likewise found that in the case of Agaricus campestris 

 the normal and anaerobic respiration of fungi containing mannite 

 took place without the formation of hydrogen, and regarded it as 

 clear that the hydrogen found by Miintz was due to the activity 

 of bacteria. In a later publication (1907^ : 188) he stated that no 

 trace of ethyl alcohol was found during the anaerobic respiration of 

 Agaricus campestris, and hence the process is distinct from zymase 

 fermentation. 



Summary. — Practically all the yeasts and molds and the great ma- 

 jority of bacteria are more or less aerobic in nature. They may live 

 and even carry on certain functions for a time under anaerobic con- 

 ditions, but growth for an indefinite period is impossible. In the soil 

 especially it seems probable that many of them live and function un- 

 der conditions alternately aerobic and anaerobic. A considerable 

 number of bacteria are obhgate aerobes, as well as some yeasts, and 

 are able to withstand the absence of oxygen for but a short time. 

 The obhgate anaerobes are practically all bacteria, some of which 



