i8o METABOLISM 



(Heinsius, 1901), in other cases, by the entry of the nutritive solution ; and in 

 Bacteria and Cyanophyceae especially, the protoplasm appears to be extra- 

 ordinarily permeable. In addition to its osmotic effect the nutritive solution 

 may have as well a poisonous action when certain variable concentrations are 

 reached. A 10 per cent, solution of alcohol is in general injurious to Fungi, 

 while a 2-4 per cent, solution is usually nutritive ; the maximum for butyric 

 acid lies much lower, i. e. about 0-4 per cent. In such cases it is conceivable 

 that the different organisms behave in different ways, and a certain form might 

 be able to tolerate a gradually increasing concentration, which would be fatal 

 if suddenly applied (compare Meissner, 1902). 



Lastly, let us glance at the influence of temperature. As Thiele (1896) 

 has shown, the temperature maxima suitable for the growth of Penicillium lie 

 at variable heights according to the food materials provided ; development 

 ceases about 31° in the presence of grape sugar, with formic acid at about 35°, 

 and with glycerine at about 36°. Formic acid has, therefore, a greater nutritive 

 value at high temperatures than glucose, whilst at ordinary temperatures it is 

 nearly the worst, the glucose proving itself the best source of carbon. 



All the points above indicated, and many others as well, must be 

 taken into account in any renewed investigations if exact results are to be 

 obtained as to the comparative nutritive value of the different compounds of 

 carbon. Though definite results have by no means been obtained in all cases, 

 still, from the researches already carried out, it may be concluded that a large 

 number of compounds may act as nutrients to Fungi, but that their value is 

 very unequal. The nutritive value of these compounds depends obviously on 

 the nature of the compound itself, but the special peculiarities of the organism 

 which it nourishes are also of importance. This latter condition becomes es- 

 pecially apparent when we compare ordinary Fungi, which we may term 

 omnivors, on account of their ability to nourish themselves with the most varied 

 food materials, with specialists, that is to say, such forms as are compelled, 

 during their life, to use certain definite substances as food. Thus Mycoderma 

 aceti thrives well on alcohol and acetic acid, substances which are of little 

 value to other Fungi. Bacillus perlihratus, according to Beijerinck (1893), 

 grows exceedingly well in acetic and malic acids, but seems to be unable to 

 assimilate tartaric acid, whilst this latter substance is, as a rule, a better food- 

 stuff and is especially acceptable to Bacillus cyanogenus. Many similar 

 examples might be adduced, and we shall meet with other cases of 

 'specialism' in the course of our studies. 



At the same time it must be remembered that there are many organic 

 substances which are useless even to the most thoroughly omnivorous types. 

 Nageli carried out experiments (1879) with the view of finding what part 

 was played by the constitution of the compounds in determining whether 

 they could be assimilated or not. It appeared that carbon could be assimi- 

 lated whether it occurred in the combination CH2 or CH ; in the combination 

 CHOH it proved injurious, and when present as CO or CN it was found to be 

 quite useless (Nageli, 1879, 401). There are, however, many exceptions 

 known to this rule (Reinke, 1883, Diakonow, 1887, Beijerinck, 1901) ; thus, 



NH C-OOH 



for example, urea CO < -vttt- and oxalic acid I are capable of nourish- 



^"2 C-OOH 



ing certain organisms, and we may yet, by careful research, be able to show 

 that carbon may be assimilated when in combination with nitrogen. At present 

 we are forced to the conclusion that the constitution of the compounds 

 is not nearly so important as Nageli supposed. That this is so is shown 

 by the fact that Fungi are able to obtain all their organic food just as 

 well from methane derivatives (glucose) as from benzol derivatives (quinic 

 acid). On the other hand, as the results of careful observation, it has been 

 shown that Fungi possess an extraordinary capacity for distinguishing sub- 



