November 26, 1891] 



NA TURE 



75 



work is done against resistance only, as in lighting glow- 

 lamps, is equal to the mean square of the current multi- 

 plied by the total resistance in circuit. 



In the chapter on the electro-magnet in surgery, Dr. 

 Thompson, as was to be expected, gives a careful sum- 

 mary of the history of the subject. It seems that hitherto 

 the principal use has been in ophthalmic surgery, for the 

 extraction of small particles of iron from the eyeball. 

 A very interesting case is narrated, in which the author's 

 brother, Dr. Tatham Thompson, of Cardiff, successfully 

 removed, by a magnetic probe constructed according to 

 his own design, a fragment of iron which had passed 

 through the eye of a blacksmith and lodged in the retina. 

 The probe, excited by a coil, was inserted through the 

 vitreous humour of the eye along the track of the wound, 

 and catching the bit of steel, drew it from its resting-place 

 in the retina. With the exception of a slight limitation 

 of the field of vision, the patient perfectly recovered his 

 sight. 



The writer has a lively remembrance of being present 

 some years ago at a search made, by means of a magnetic 

 probe which he had arranged for one of the surgeons of 

 Glasgow Infirmary,for a fragment of iron which was alleged 

 to have entered the knee of a blacksmith. The blacksmith 

 was exceedingly lame, and an examination of the knee 

 by means of a magnetometer for signs of the presence of 

 iron had resulted in some very puzzling indications. All 

 iron, it was thought, had been removed from the patient, 

 and with the knee in certain positions very decided in- 

 dications of magnetized iron or steel had been observed. 

 The probe, magnetized by a battery current, was inserted 

 in an incision made at the place where the iron was sup- 

 posed to have entered, but without effect. An adhesion 

 was found to exist in the joint, and was broken down by 

 the surgeon, with the result that after the patient's re- 

 covery the lameness had disappeared. It was found on 

 stripping the patient that he wore a truss, and hence the 

 magnetometer effects ! 



It seemed rather unlikely, in any case, that the magnetic 

 probe would be effective in removing a splinter deeply 

 embedded in muscular tissue. 



The last chapter, on permanent magnets, though no 

 part of the subject-matter proper of the book, is never- 

 theless very complete, and full of valuable information 

 regarding the magnetizability of different kinds of steel, 

 effects of temperature, use of laminated magnets, lifting 

 power of magnets, and permanence of magnets with 

 lapse of time. 



The chapter concludes with a short sketch of 

 astatic arrangements of needles. In connection with 

 these, it may be remarked that the vertical pair of 

 astatic needles— which has the advantage- of perfect 

 and permanent astaticism, inasmuch as each needle is 

 astatic— was described, with other astatic arrangements, 

 in a paper by Mr. T. Gray and the present writer, in the 

 Proceedings of the Royal Society for 1884 (vol. xxxvi.). 



Here we must take leave of a most interesting volume. 

 The outside of the book is tastefully got up, the printing 

 and paper are excellent, and the whole is worthy of the 

 reputation of both author and publishers. 



A. Gray. 

 NO. 1 152, VOL. 45] 



FUNGUS EA TING. 

 British Edible Fungi : how to Distinguish and how to 

 Cook them. By M. C. Cooke. (London : Kegan Paul, 

 Trench, Trubner, and Co., 1891.) 



THERE is a fascination in the minds of many people 

 for the eating of fungi, which has often been ex- 

 pressed in popular books on the subject by authors of 

 various degrees of power. Some of these are enthusiasts, 

 who suffer palpably from that malady of intolerance which 

 characterizes so many propagandists, who would persuade 

 us that those things are best to eat and drink which they 

 have found so ; others, again, temper their recommenda- 

 tions by the calm arguments of the scientific man, though, 

 speaking as having found, they must write with a tinge of 

 that persuasiveness necessary to overcome wide-spread 

 prejudice, or ignorance, if they are to be understood by 

 the multitude ; others, again, are content to state the 

 facts, and let the logic of their sentences make its own 

 impression in due course. 



It is not easy to say off-hand in which of these categories 

 the writer of the book under review should be classed, nor 

 is it of much consequence to look at his writings according 

 to the decision arrived at in that connection. It is cer- 

 tainly no more than fair to say that Mr. Cooke has com- 

 piled a little book of no small value as a guide to common 

 edible fungi of this country ; and that, while the informa- 

 tion is singularly clear, and told in plain and homely 

 language, it loses little or nothing in the simple telling, 

 so far as the facts about these cryptogams are concerned. 

 In so far, the author's well-known reputation as a myco- 

 logist is not likely to suffer ; but it must be added that, 

 while we do not pretend to criticize in detail all that 

 relates to the cooking of these delicacies, and while it 

 must always be more or less a matter of individual 

 opinion whether Champignons stewed with pepper and 

 butter, or Boletus with sauce of lemon-juice and powdered 

 lump-sugar, are the more delicious, there is something 

 that smacks of prejudice in the more than hearty com- 

 mendation of some of the cooked favourites. Be this as 

 it may, Mr. Cooke is unquestionably a high authority on 

 his subject, and he has done good service in supplying 

 the public with a well-written account of it, and with ex- 

 cellent coloured drawings of about forty of the chief 

 forms of edible fungi. 



Few people in this country are aware that nearly two 

 hundred of the things called toadstools are at least edible, 

 and fewer still will be prepared to believe that there are 

 people in the world who regard some fifty-odd of these as 

 dainties. Mushrooms, truffles, and morels exhaust the 

 list for most Englishmen, and many are dubious about 

 even these, and eat them, when served, with various 

 degrees of trustful confidence, or the reverse. 



It is a severe shock to these persons when they learn 

 that such species as Amanita rubescens, Lepiota procerus, 

 Coprinus comatus, and other " horrid toadstools," may not 

 only be eaten, but are even extolled as delicious ; and when 

 it comes to recommending the green-topped Clitocybe 

 odorus, smelling of anise, or the purple Tricholoma 

 nudus, and other violently coloured species, the amateur 

 may be pardoned for hesitating. Nevertheless, these and 

 many other forms popularly held as dangerous are not 

 only edible, but are also capable of distinction with a 



