i8o 



NATURE 



[April 27, 1916 



Tuberculosis : A General Account of the Disease; 



Its Forms, Treatment, and Prevention. By Dr. 



A. J. Jex-Blake. Pp. viii + 231. (London: 



G. Bell and Sons, Ltd., 191 5.) Price 2S. 6d. net. 

 An excellent account of the subject of tuberculosis 

 is g"iven in this book, free from technicalities, so 

 that it should be easily intellig-ible to those who 

 possess no special education in medical or 

 scientific matters. 



The opening- chapter deals briefly with the his- 

 torical side of the subject, and then the tubercle 

 bacillus is discussed. The different types of the 

 bacillus are described — their occurrence and re- 

 lationship to the disease in man — and a summary 

 is given of the vexed question of the infection of 

 man from bovine sources, in which both sides 

 of the controversy are placed before the reader. 



Predisposition and immunity, the paths of in- 

 fection, and the statistics of tuberculosis are next 

 dealt with, after which a general account is given 

 of the -disease as it attacks various parts of the 

 body. 



The subjects of- prog^nosis and general treat- 

 ment are discussed, and the book ends with de- 

 scriptions of tuberculin and sanatorium treatment 

 and suggestions for the prevention of the disease. 

 The author throughout avoids extremes, and when 

 there is a difference of opinion both aspects of 

 the question are stated. The book contains a 

 large amount of upy-to-date information, and is a 

 very useful summary; it should appeal to a wide 

 public. R. T. H. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The West Indian Firefly. 



The writer is not in any sense an entomologist, 

 but for this very reason his notes regarding this insect 

 may have a certain interest as being from a different 

 point of view from that usually taken. The beetle is 

 much brighter than those with which we are familiar 

 in the States and in England, and is always a source 

 of interest to travellers. They first appear in Jamaica 

 about the middle of February, and by the middle of 

 June are found in great numbers, so that the fields 

 as seen from a slight elevation sometimes appear 

 strewn with wandering stars, much brighter than 

 those in the heavens above. They are particularly 

 numerous on damp or foggy evenings when there is 

 no moon. Their light is constantly fluctuating, and 

 the fluctuations occur more or less in unison over a 

 considerable area, which makes their appearance much 

 more striking. An individual light is readily seen at 

 a distance of a quarter of a mile. They have power- 

 ful jaws, but nevertheless fall a ready prey to spiders, 

 who consume them in large numbers. 



The insect varies somewhat in size, but on the 

 average measures 30 mm. (one and a fifth inches) in 

 length, by 9 mm. in breadth, and is of a dark brown 

 colour. Its system of lights is peculiar, and quite un- 

 like the northern species. It carries a green light on 

 either shoulder, and a much brighter orange light 

 beneath the abdomen. This latter, however, is never 

 shown except in flight, and at the very moment of leav- 

 NO. 2426, VOL. 97] 



ing the ground. One often sees' them flying along th( 

 side of a house, illuminating the eaves or clap-board 

 ing with this bright orange light, much as a mar 

 might do it with a dark lantern, evidently looking 

 for food. 



When attacked by a spider their light glows in- 

 tensely and continuously under the intluence of tht 

 poison. If crushed, the light continues to glow lon^ 

 after the creature is dead, but it can be shut off ai 

 will. If held in the hand while the light is turnec 

 on, the insect gives out a perceptible warmth, and 

 on enclosing one in a wine-glass with a thermometei 

 bulb, the mercury was found to rise 1° F. the first 

 minute. It rose another degree the second minute, 

 and o-6° in three minutes more. After this it slowlj 

 fell, although the light was still shining. Later, after 

 the light had been extinguished, the thermometei 

 returned to its original temperature, usually between 

 70° and 75°. Some fireflies are much more vigorous 

 than others. With a weakly one the thermometer maj 

 not rise even as much as 1° in all. Two seem to be 

 no more efficient in this respect than one. 



The writer would like to have kept one a 

 prisoner for twenty-four hours, weighing it at interl 

 vals, its loss of weight indicating the amount of it.'j 

 normal food consumption. Since its bulk, however, i; 

 but 07 of a cubic centimetre, its weight is abr 

 07 of a gram, and its food consumption would be 

 small that it would require a delicate chemical balan 

 to determine it with any accuracy. Such an instr 

 ment is not available here, so this investigation mi. 

 be left to someone else. Presumably, however, it e; 

 about as much as other beetles of the same size. 



On account of its only showing its brightest lig 

 when in flight, its candle-power is rather difficult 

 determine. This was accomplished indirectly, ho- 

 ever. A great number of them fly along a neighboi; 

 ing road, and their position can be determined '' 

 their illumination of the enclosing stone walls. Th( 

 brightness was found to equal that of the St 

 Canopus, which was just over the road, and at rath' 

 a low altitude. Its brightness was at that time equ 

 to a Orionis, the altitude of which was 40°. It w 

 a very clear evening, as is generally the case here, ' 

 that we may take the brightness of the latter as 

 10 magnitude. The distance of the road was 175 f'l 

 or 53 metres. A zero magnitude star is equal to 01; 

 candle-power at 526 metres. If of zero magnitu<j 

 the light of the fireflv would therefore have been ju 

 001 of a candle-power. Being of first magnitude, i, 

 light was 0004 c.p. This result is probably corrfj 

 within half a magnitude, or 50 per cent., and coj 

 sidering the apparent brilliancy of the insect is smalli 

 than one would have expected. The writer is r; 

 aware of any previous measures of this ounntity. j 



William H. Pickeringj 



Harvard Astronomical Station, Mandeville, 

 Jamaica, B.W.I. , March 22. 



"Optical Glass" and Fluorite: An Ethical Note. 



Mr. F. J. Cheshire's letter in Nature of March i' 

 recalls the most excepti6nal character of the publi'- 

 tion by Prof. Abbe and the firm of Zeiss of that c- | 

 covery of apochromatism for which all must still p | 

 grateful. For the details I refer to the Journal' 

 the Royal Microscopical Society, ser. 2, vols, vi., v. 

 1886-7. An article in vol. vi., p. 3i5f, "The N'' 

 Objectives," is evidently based on the letter of "'• 

 Abbe of March 4 (cited by Mr. Cheshire), for it c- 

 j tains precisely the same window-dressing stateiii^ 

 i that optical glasses hitherto in use only contain , 

 ! chemical elements, while the new objective contf. 

 . not fewer than fourteen. This article throughout j^' 

 [ veys the impression that it has been alone the util'' 



