May 26, 192 1] 



NATURE 



395 



with the following observations. When a short inter- 

 ruption is made in a musical note it is not a beat (i.e. 

 a short silence) that is heard, but, on the contrary, a 

 short noise which appears to add itself to the un- 

 interrupted note. The way this short interruption is 

 produced and an explanation of the noise that results 

 according to the resonance theory of hearing will 

 be found in the British Journal of Psychology (vol. xi., 

 192 1, p. 277). 



If, then, in order to change the phase of a note 

 by 77, the usual interval between successive impulses 

 is altered from r to rx'i, the beat (i.e. the silent 

 interval) which the observer hears cannot be due to 

 the mere interruption in the sequence of the waves, 

 because experiment shows that such an interruption 

 would be heard as a short noise. But, further, even 

 if Dr. Perrett's explanation could be accepted for the 

 case where the interval is increased from r to r x if, 

 it clearly could not, I think, apply to the case where, 

 in order to introduce a change of phase of n-, r is 

 reduced to r/2 ; for on Dr. Perrett's reasoning no beat 

 should be evident in this case, whereas experiment 

 shows it to be present. " H. Hartridge. 



King's College, Cambridge. 



Haemoglobin in Mollusca. 



Sir Ray Lankester will find some interesting 

 experiments on the usefulness of haemoglobin to 

 Planorbis and Chironomus larvae in a paper by Leitch 

 in the Journal of Physiology (vol. 1., 1916, p. 370), 

 in which the author indicates that its respiratory 

 value comes into play only when the oxygen pressure 

 is quite low. This does not, of course, solve the 

 problem as to why there should be various closely 

 allied mollusca (Limnaea) living side by side with 

 Planorbis, and with apparently equal success, which 

 have no haemoglobin beyond a trace in the muscles of 

 their lingual apparatus. The possession of a con- 

 siderable quantity of haemoglobin seems to be a 

 generic character, since it is present in all the species 

 of > Planorbis, which differ a good deal among them- 

 selves in their habits and in their capacity to live in 

 clean and dirtv water, and absent in all sorts of 

 Limnaea. Sir Ray Lankester seems to have forgotten 

 what he taught me in his elementary class twenty-six 

 years ago : that haemoglobin has come to have 

 secondary (decorative) uses in man ; but he will 

 perhaps be as loath to admit an aesthetic sense in 

 snails and their companions as he has been to accept 

 the selective intelligence of Earland's foraminifera in 

 building their tests. But the albino form of Planorbis 

 corneas found by Mr. W. T. Webster near Barnet, 

 in which the colour of the haemoglobin is not 

 obscured by black pigment, is certainlv a gorgeous 

 spectacle. A. E. Boycott. 



17 Loom Lane, Radlett, May 14. 



Physiological Reactions in the Protozoa. 



It would be deplorable if the letter by Mr. Ludford, 

 and with the address of a zoological laboratory 

 (Nature, May 12, p. 332), should be thought by any- 

 one to represent the attitude of zoologists in general 

 or of protozoologists in particular towards physio- 

 logical problems. It would be hard to find a more 

 individualistic reaction than the "grouping" of 

 Protozoa in direct response to a particular chemical 

 or physical stimulus. Typical experiments are 

 described in every physiological or protozoological 



NO. 2691, VOL. 107] 



text-book, and it requires some imagination to see 

 in such behaviour " the dawn of a gregarious 

 instinct." 



It is difficult to understand how any student of 

 zoology or biology could have written the sentence 

 beginning "On the part of Protozoa, protection 

 against toxins in the water is a necessary precaution 

 that has to be taken to safeguard the individual " 

 (italics mine). Do the Protozoa really practise sani- 

 tary science, and are they no longer subject to natural 

 selection? J. s. Dunkerly. 



Zoology Department, The University, 

 Glasgow. 



Picture-hanging Wire. 



In reference to Mr. Marston's letter upon the above 

 subject (N.ature, May 19, p. 362), I have for many 

 years past used and advocated the use of plain copper 

 wire in preference to any other means of suspension. 

 The only matter that calls for careful attention is 

 avoidance of "kinks." With heavy pictures my prac- 

 tice is to have two entirely independent suspensions 

 — scre\v-eyes, wire, and wall nail or hook — the dupli- 

 cate being entirely screened by the picture, and either 

 actually or so nearly sharing the weight that should 

 the other suspension fail it could take the whole load 

 at once without jar. 



If I use a (nailed-on) wall-hook I put a stout nail 

 immediately beneath to provide against failure of the 

 brass hook, and I have found it a good plan when 

 using a brass-headed nail to drive in a wire nail at 

 a steep angle beneath it so that the head of the wire 

 nail lodges beneath the brass head. The wire nail 

 acts excellently as a strut. A. J. Stubbs. 



Anode Rays of Beryllium. 



The method of anode-ray analysis which was used 

 to determine the isotopes of' lithium (Nature, 

 February 24, p. 827) has recentlv been applied to 

 the case of beryllium. A well-marked parabola was 

 found corresponding to a single charge and an atomic 

 weight 90 + 0-I (Na = 23). No second line was ob- 

 served which could with certainty be attributed to 

 beryllium, but the parabola at 90 "was not so strong 

 as that at 70 for lithium, and it is doubtful if one 

 of a tenth the intensitv could be observed. On one 

 plate a scarcely perceptible indication of a line was 

 found in the neighbourhood of 10, but as more recent 

 photographs, in which the line at 9 was stronger, did 

 not show it, it seems likely that it was not due to 

 beryllium. No indication "was found which would 

 suggest that the atom of bervlHum can lose two 

 electrons under the conditions of these experiments. 



G. P. Thomson. 



Cavendish Laboratory, Cambridge, Mav 23. 



The Colours of Primroses. 



May not Dr. Heslop Harrison's experiences of 

 primulas (N.ature, May 19, p. 359) be due to the 

 influence of cold and somewhat resemble what is seen 

 in our so-called copper-beech in the spring and early 

 summer? Few seem to be aware that during the 

 summer its characteristic colour entirely disappears 

 and it then has the ordinary green foliage. Other 

 plants, too, e.g. some varieties of roses, show the 

 same sensitiveness. G. Abbott. 



May 24. 



