204 



KNOWLEDGE. 



June, 1913. 



into new lines over and over again. The well-worn 

 simile of the tree and its branches will once more 

 serve to illustrate this. The "tree of the Green Algae " 

 has its trunk represented by the main line of evolution 

 from the Flagellata, and then it may be supposed to 

 branch into three — thethree lines which have been con- 

 sidered. The Volvocine branch is probably short and 

 with little ramification ; the others fork repeatedly, 

 producing finer and finer branches and twigs. The 

 leaves of the tree alone represent existing forms, but 

 here the simile rather breaks down ; for it must be 

 supposed that the leaves nearer the top of the tree 

 are more highly evolved than those lower down. 

 The trunk and branches are obscured in the mists of 

 the past, and our problem is to indicate these from 

 a knowledge of the leaves alone. The postulated 

 arrangement of the leaves must give considerable 

 help, but the impossibility of complete solution is 

 patent. 



It must be remembered that not one of these 

 proposed modifications in evolution has actually been 

 observed to take place, and the position and basis 

 of the scheme are theoretical. It is quite impossible 

 to dogmatise on any problem of evolution, at least 



in the present state of our knowledge, and different 

 schools of thought may read quite a different inter- 

 pretation into the facts. 



The forms which have been considered here are 

 all characterised by the bi-ciliate type of zoospore or 

 gamete, with equal cilia, when any are produced, and 

 this has been thought of sufficient importance to 

 mark off the group, which has been called the 

 Isokontae by Blackman and Tansley. Space does 

 not permit of the discussion of the other groups, but 

 there is evidence that the " coloured seaweeds " have 

 been evolved directly from coloured Flagellates, 

 while the Oedogouium forms and the Conjugatae, 

 including the Desmids, and so on, may have sprung 

 from the Isokontan stock. 



It is impossible to doubt the great fact of pro- 

 gressive evolution when confronted with this and 

 similar series of organic types. Most of the great 

 underlying principles and laws of the process are 

 still to be elucidated, however. The Algae appear 

 to be still plastic, and further study and observation 

 should at least help us to grasp some of the forces 

 and influences which are at work in the production 

 of a new species in the world flora. 



ELECTRICAL CONDUCTIVITY IN THE SERVICE OF BACTERIOLOGY. 



By DR. ALFRED GRADENWITZ. 



Interesting experiments have recently been made by Dr. 

 M. Oker-Blom, Professor at Helsingfors University, on the 

 possibility of utilising the electrical conductivity of bacteria 

 cultures for obtaining useful data on the nature of bacteria 

 and the biological phenomena occurring in these cultures."' 



The electrical conductivity of an electrolyte is known to be 

 reduced by the presence of non-conductive substances such as 

 sugar, albumen, and so on, the more so as the amount of these 

 substances is greater. This reduction of conductivity has 

 further been shown to depend on the nature both of the 

 electrolyte and the non-electrolyte, being accounted for by 

 some sort of friction between the ions and non-conductive 

 molecules. If, now, a culture solution containing albumen or 

 sugar, or both of these, be submitted to such conditions that 

 these substances will undergo chemical scission, the con- 

 ductivity of the system is bound to be influenced in some 

 way or other. On one hand, the conductivity of the culture 

 liquid is increased by reducing through chemical scission the 

 amount of non-conductive substance ; if, however, the sub- 

 stances newly formed should likewise be non-electrolytes, the 

 total amount of non-conductive substance in the solution will, 

 as a matter of fact, be increased, and variable effects will be 

 observed according to circumstance. Far more marked effects 

 are, however, obtained whenever new electrolytes are produced 

 in the liquid, and as acids and alkalis are the most highly con- 

 ductive of these, any variation in the acidity or alkalinity of a 

 culture liquid as produced by bacterial influences is bound to 

 manifest itself in the conductivity of the liquid. 



Dr. Oker-Blom has made three parallel series of experi- 

 ments comparing the respective influences of two bacteria 

 (Bacterium coli and Bacterium typhi) on the electrical 

 conductivity of culture liquids. The glass vessels used in 

 this connection had been specially constructed on his sugges- 

 tions, and contained strictly equal amounts of liquid. After 

 their inlet and outlet openings had been stopped with small 



pads of wadding, they were introduced into a water thermostat, 

 maintaining them at any constant temperature desired, where 

 the electrical conductibility of the liquid could be watched at 

 any moment. 



The curves reproduced in the original memoir give an 

 excellent idea of the behaviour shown by the conductivity of 

 culture liquids under the influence of the two bacteria. In 

 the first series the conductivity curve of the coli bacteria is 

 found to rise considerably already after two days, and even 

 more rapidly on the third and fourth days, in order afterwards 

 only to rise by degrees somewhat further. The conductivity 

 curve of typlii bacteria shows a quite different behaviour. 

 After exhibiting, during the first five days, only a slight tendency 

 to rise, it will rise abruptly on the fifth day, and continue 

 rising in a marked degree from the seventh to the tenth day. 

 After a slight further rise, it eventually approaches towards 

 the coli curve, though not reaching it entirely during an 

 eighteen days' experiment. The two curves show between 

 the second and the fifth day the greatest mutual departures. 



The liquid used in this connection was Fraenkel's culture 

 liquid, with a slight addition of soda. The two other series of 

 experiments, made with the same liquid, containing one per 

 cent, of lactose and glucose respectively, gave quite similar 

 results. During the first two days a very satisfactory agree- 

 ment between the curves of conductivity and those of acidity 

 or alkalinity was noted. 



These experiments go to show that the bacteriological 

 variations in the electrical conductivity of culture liquids are 

 really determined by products of chemical scission (neutral, 

 alkaline or acid). Though, being only the collective expression 

 of bacterial decomposition, the electrical conductivity thus 

 gives a fairly good idea of the actual phenomena, and as the 

 conductivity curves for each kind of bacteria show some 

 specific features, they might prove useful in detecting these 

 bacteria for the purposes of diagnosis. 



Centralblatt f. Bakt., etc., I., Numbers 4-5, 1912. 



