1881.1 



MICROSCOPICAL JOCTRNAL. 



207 



Again, in a paper on " The Rela- 

 tions between the Development, Re- 

 production and Markings of the 

 Diatomaceae," read before the Royal 

 Microscopical Society in January, 

 1877, by the same author, the osmotic 

 theory of motion was again discussed, 

 and the belief expressed that careful 

 observation would in due time re- 

 veal the presence of motile filaments ; 

 just as the actual presence of the 

 previously unseen but long suspected 

 fiagellum in Bacterium was at last 

 detected by Messrs. Dallinger and 

 Drysdale. 



Still later, at the close of a paper 

 entitled " Are the Desmids and Dia- 

 toms Simple Cells ? " published in 

 the Popular Science Review for April, 

 1877, the same views are repeated in 

 relation to the general question in- 

 volved in the various well-known ex- 

 tra-frustular appendages observable 

 in certain genera of diatoms. 



In this connection, there is here 

 given a copy of one of Dr. Wallich's 

 original notes of observations on the 

 motion of Nitzschia closterium, made 

 in i860, from which his conclusions 

 were drawn. 



" In some material obtained Feb. 

 2d, 1863, from the Aquaria at the Zoo- 

 logical Gardens, I found a long, 

 beaked variety of Nitzschia closte- 

 rn/w, length -^ of an inch = .0120. 

 Diameter at centre of valve ^^V^ inch. 

 Diameter of beak, ^ g^o inch. Spe- 

 cimens of this Nitzschia moved about 

 very rapidly and laid hold, during 

 their progress, of masses of foreign 

 matter — apparently vegetable debris 

 — many times the weight of the dia- 

 tom itself. These they pulled along, 

 now and then retaining their hold 

 and towing the masses along behind 

 them at a considerable distance from 

 the extremity of the beak. In one 

 example the mass was nearly \ of the 

 total length of the Nitzschia, and at 

 least a third as broad as its broadest 

 part. This mass was moved half- 

 way across the field of vision, and 

 several times tugged after the diatom. 

 The most remarkable feature being 



the ease with which the long, slender 

 organism turned round, sometimes 

 with a steady, gliding motion, some- 

 times with forcible jerks, as if there 

 was resistance or pressure to be over- 

 come. To my mind it was quite im- 

 possible to witness what took place 

 without feeling perfectly convinced 

 that the foreign body was in some 

 way laid hold of by a motile filament 

 or may be several filaments, given off 

 from the diatom, and in the case in 

 question serving the purpose of a tow 

 rope. I had many years previously 

 arrived at the conclusion that such 

 filaments exist in the Diatoms gener- 

 ally, although unable to detect them 

 with the aid of Ross's -^ and -^ 

 most perfect objectives. It is utterly 

 absurd to suppose that such move- 

 ments as I witnessed could, by any 

 possibility, be due to osmotic action. 

 See my paper on 'The Distribution and 

 Habits of the Free-floating Pelagic 

 and Fresh-water Diatomaceae' pub- 

 lished in The Annals and Magazine of 

 Natural History for January, i860, 

 where the question of these move- 

 ments, etc., is fully described." 



T. D. C. 



Koch's Demonstrations in the 

 Germ Theory.* 



Among the many interesting facts 

 brought forward and the discussions 

 held during the Congress, none sur- 

 passed, if indeed any equaled, the 

 work done by Dr. Robert Koch, of 

 Berlin. He first showed some of the 

 new methods of cultivation, which 

 surpass in beauty and simplicity, as 

 well as in usefulness, anything that 

 has yet been done in this way. He 

 began to study the growth of pig- 

 ment bacteria on boiled potatoes, and 

 soon discovered that, as the organ- 

 isms were there growing on a firm 

 substratum, they did not become 

 mixed up with each other or with ac- 

 cidental contaminations, and he could 

 always find a spot where the bacte- 

 rium was pure. Any organism intro- 



* From the Medical Herald. 



