504 



BIOLOGY OF THE MICRO-ORGANISMS. 



Nageli 's 

 experiments. 



Substances 

 Huitable for 

 supplying the 

 necessary 

 nitrogen. 



If Raulin sowed spores of Aspergillus niger in this fluid, 

 which was kept at a temperature of about 35 C. in shallow 

 covered vessels in a layer 2 to 3 ctm. in depth, a fructifying 

 mycelium was formed after three days ; this was removed, and 

 from the remaining fluid a new crop was obtained after three 

 days more. After the removal of this second crop the nutrient 

 materials of the fluid seemed to be almost entirely exhausted. 

 The weight of the total growth when dry was determined, and 

 was found to amount to about 25 grms. This result was 

 compared with that obtained when one or other of the con- 

 stituents of the normal nutrient solution was omitted. 

 Raulin found that the absence of phosphoric acid had the 

 greatest influence, the resulting growth being reduced to ^w 

 part of the normal ; that the absence of ammonia diminished 

 the growth to ^ ; and of potash to ^. No constituent of 

 Haulm's fluid could be omitted without harm; even the 

 omission of the zinc had a marked influence on the result. 



More complete experiments of a similar character 

 have recently been made by Nageli. He showed that 

 there were certain sources of error in the former experi- 

 ments ; that, for example, sufficient care had not been 

 taken to secure pure cultivations and to exclude all other 

 organisms ; that, further, the access of air, the reaction, 

 the most favourable concentration of each of the nutrient 

 materials (the so-called "optimum of concentration"), 

 and, finally, the alteration of the nutrient solution by the 

 growth of the fungus itself, were not sufficiently taken into 

 account. Nageli's* numerous and exact experiments 

 led to the following results : 



The necessary nitrogen cannot be obtained from free 

 nitrogen, nor from the nitrogen which is in combina- 

 tion with carbon in cyanogen ; in like manner nitrogen 

 in combination with oxygen seems to be unsuitable, at 

 any rate nitre-compounds, such as picric acid and nitro- 

 benzoic acid, were very bad nutrient materials. On the 

 other hand, the best forms seemed to be the NIL 

 groups; the NH group was less suitable. In corre- 

 spondence with this, the best materials for the nourish- 

 ment of the fungi were : ammoniacal salts (sal ammoniac, 

 phosphate of ammonia, nitrate of ammonia ; acetate, 

 oxalate, succinate, and tartrate of ammonia, &c.) ; also 



* Nageli, Vntersuchungen iiber niedere Pilze, Munich, 1882. 



