542 



NATURE 



{Oct. 3. 1889 



eventually, upon the total retraction of pseudopod, they 

 are deposited on the substance of the organism. Thus 

 the " house " is built by purely mechanical means, without 

 any " intelligence " or " volition " on the part of Diffliigia. 

 In the Co7itemporary Review for April 1873, the late 

 Dr. Carpenter alluded to similar habits of a certain 

 marine Protozoa, saying : " The deep-sea researches 

 on which I have recently been engaged have not exercised 

 my mind on any topic so much as on the following." He 

 then describes what he regarded as a selective choice by 

 the Protozoa of faier particles of sand by some species, 

 and coarser particles by other species, for the purpose of 

 building into the structures of their shells. No doubt, 

 however, if the process were carefully observed, it would 

 be found that this apparently selective choice is really due 

 to the size or quality of the adhesive drops on the 

 pseudopodia, which may very well differ slightly in these 

 respects among the different species. 



Much the larger portion of Dr. Verworn's work is, as 

 its title conveys, occupied with an account of his experi- 

 mental researches. These are thoroughly systematic and 

 fairly exhaustive. First there are thirty pages describing 

 the natural or spontaneous movements characteristic of 

 well-known forms belonging to all the main divisions of 

 the Protozoa, Next there follow a hundred pages dealing 

 with the author's experiments in stimulation, arranged 

 under the headings — luminous, thermal, mechanical, 

 auditory, chemical, and electrical. Lastly, there are over 

 fifty pages describing a number of experiments in various 

 forms of section and artificial division of sundry 

 unicellular organisms. The whole of this part of the 

 research is exceedingly good, and must be studied by 

 everyone who is engaged in practical work. From this 

 point of view the two most interesting facts are, we think, 

 the following. It is a general law of excitable tissues that 

 the principal seat of excitation is the kathode on closing 

 a galvanic circuit, and the anode on opening it. But Dr. 

 Verworn finds that among the Protozoa the reverse of 

 this otherwise general rule obtains. It appears that this 

 curious observation was first made by Kijhne as long ago 

 as 1864 ; but Dr. Verworn has done good service in now 

 calling attention to it, corroborating, and extending it to 

 other unicellular organisms. 



The second fact to which we allude is, that when a 

 galvanic current is closed through a drop of water 

 containing a number of Protozoa {e.g. Parameciitm^ 

 Coleps, Colpoda, Stentor, Halteria), they will all begin to 

 travel rapidly and directly to the negative pole, and, if the 

 current be left closed for a few seconds, will all become 

 congregated thereat. On now opening the current they 

 will all begin to travel towards the positive pole, but then 

 soon segregate. It was proved that this is not any merely 

 physical phenomenon, but a truly vital one : the Protozoa 

 of the genera named will invariably swim towards the 

 kathode on closing, remain at the kathode so long as the 

 current continues to pass, and swim towards the anode as 

 soon as the current is opened. Even when the kathode 

 is a copper wire, which causes the death of all the 

 Protozoa that approach it, they will equally well con- 

 gregate in its vicinity, there to perish ; and by using a 

 movable kathode of harmless material, the Protozoa 

 may be led about like a flock of sheep following their 

 shepherd. To this curious physiological property on the 



part of Protozoa, Dr. \'erworn has assigned the name 

 " Galvanotropism." But one would like to be informed 

 as to the strength of the current employed, e.g. if it were 

 sufficient to induce electrolysis. If the current used was 

 a very weak one, would it not be interesting to try the 

 effect of greatly strengthening it ? 



The experiments in section were all devoted to testing 

 the value of the nucleus as a co-ordinating centre of 

 movements, ciliary and otherwise. The results were 

 uniformly opposed to the views of Rossbach, Engelmann, 

 and others who have regarded the nucleus in this light — 

 the un-nucleated portions of several Protozoa continuing 

 to exhibit all the same spontaneous movements as the 

 nucleated. It is to be regretted that the author did not 

 more completely extend these researches to an investi- 

 gation of the functions of the nucleus in respect of nutri- 

 tion and regeneration, where so much still remains to be 

 done. But we may hope that this is perhaps to follow. 



George J. Romanes. 



OUR BOOK' SHELF. 



Treatise on Trigonometry. By W. E. Johnson, M.A, 

 (London ; Macmillan and Co , 1889.) 



We have here a work which should prove very service- 

 able to those who are commencing the subject with the 

 hope of proceeding to more advanced mathematics, and 

 also to those wishing to revise their study of trigonometry 

 and to extend it beyond the limits of an ordinary 

 elementary text-book. 



The volume is divided into two parts, geometrical ancl 

 analytical, the former dealing with geometrical appli- 

 cations, the latter with the purely theoretical and analytical 

 side of the subject. The first part deals with the 

 properties of points and circles connected with triangles 

 and rectilinear figures, trigonometrical ratios and their 

 fundamental relations ; chapter ix. treats of the geo- 

 metry of the triangle, including the nine-point circle, 

 the cosine and ex-cosine circles ; and in chapter x. 

 we have formulae for circles and rectilineal figures. 

 In the algebraical part, logarithms, ratios of compound 

 and multiple angles, developments of formuhe for the 

 sums of angles, factorization and summation, are 

 dealt with. In chapter xviii. the proof of the binomial 

 theorem is a modification of Euler's, thereby making it 

 depend directly on the index theorem. Chapter xxi. con- 

 sists of the apphcation to trigonometrical formulae of 

 imaginary and complex quantities, and chapter .xxii. of a 

 geometrical interpretation of imaginaries. 



Short digressions have been made into geometry, 

 algebra, and theory of equations in various parts of the 

 work, thus bringing out more clearly the train of reasoning 

 that is necessary to establish and expound the principles 

 that lie at the foundation of mathematics, to which, in. 

 trigonometry, the student is first introduced. 



At the end of each chapter is a copious supply of 

 examples, and the book concludes with a set 

 miscellaneous examples and answers to the above. 



;t ^ 



\ 



ns exw 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions « 

 pressed by his correspondents. Neither can he undertak- 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Naturk, 

 No notice is taken of anonymous communications. ] 



Taming the Puma. 

 As I believe that the puma, or Rocky Mountain lion, 

 usually considered one of the most intractable ancl untamable 

 animals, the following brief account of what I have just se 



I 



