386 



NATURE 



[November i8, 1920 



nature it has to be considered whether the introduced 

 species is likely to turn to plants of economic value 

 and thus do more harm than good. It is necessary, 

 therefore, to make quite sure of this vital point before 

 introducing the Agromyzid into India. The author 

 of this memoir has brought to light a number of 

 insects attacking Lantana in India. The most 

 efficient of these appears to be a small plume moth 

 {Platyptilia pusillidactyla), the caterpillar of which 

 feeds on the flower-heads and considerably reduces 

 the number of seeds produced. Its efficiency, how- 

 ever, would be much greater were it not so subject 

 to the attacks of Hymenopterous parasites. No insect 

 is likely to do more than act as a check upon the 

 reproductive capacity of the plant, and until such 

 insects can be satisfactorily brought into operation, the 

 eradication of the plant in (at present) lightly infested 

 districts by cultural methods seems to be the only 

 feasible course. 



Recent investigation into the irregularities of the 

 heart illustrates the great value of researches which 

 apparently have no practical application. The elec- 

 trical phenomena of muscle and nerve were thought 

 to be of merely academic interest, but after the per- 

 fection of the Einthoven galvanometer these electrical 

 reactions became of great use in the study of the 

 action of the heart. By placing pairs of electrodes on 

 the surface of a muscle, as shown by the two circles 

 of the accompanying diagram, it is found that a 

 wave of excitation travelling in the 



O direction of arrow A will"* reach both 



electrodes at the same time and the 



A electrical response will be insignificant, 



but a wave of excitation travelling in 



tthe direction of arrow B will reach the 

 electrode, marked with a cross, first, so 

 B that an appreciable electrical response 



will result, and the direction of the elec- 

 trical current will indicate the direction in which the 

 wave is travelling ; the commencement of the elec- 

 trical response shows the time at which the wave of 

 excitation reaches the electrode. By this method Dr. 

 T. Lewis and his co-workers have followed the path of 

 the excitation in the disorder known as auricular 

 fibrillation (see Heart, August, 1920, vol. vii., No. 4). 

 The normal heart-beat starts at a locality known as 

 the sino-auricular node, and spreads in all directions 

 over the auricle. When the wave of excitation 

 reaches the extremities of the auricle it cannot pass 

 back because it is dammed by the refractory period 

 of the contracting auricle. In auricular fiutter the 

 wave of excitation passes down one side and up the 

 other, so that it reaches the starting point after the 

 muscle has relaxed. Thus the wave can follow in 

 the same direction and a " circus " movement becomes 

 established. The result is that the auricle beats at a 

 rate of more than 300 contractions per minute. It 

 is not known why the auricle allows the wave of 

 excitation to pass in one direction only, but once it 

 is started it continues because the auricular muscle 

 relaxes just before the wave of excitation reaches it, 

 and the wave of excitation does not catch up to the 

 refractory period of the contracting muscle. 

 NO. 2664, VOL. 106] 



Dr. J. RuNNSTROM, of the Zootomical Institute, 

 Stockholm, has long been occupied with experiments 

 on Echinoderm larvae. Among others, he has cut 

 away portions of the larvae and observed the further 

 development either in those portions or in the indi- 

 viduals from which they have been removed. In 

 Bergens Museums Aarbok, 1917-18 {1920), he tells 

 us how he has removed from the larva of a sea- 

 urchin (Parechinus tniliaris) the sunken area that 

 would in the normal course of metamorphosis produce 

 the young urchin. This did not prevent the forma- 

 tion of a new sinking or infolded sac of similar 

 character, though, owing to the regeneration of the 

 hydroccel (whence the characteristic water-vascular 

 system develops), the formation of an actual echinoid 

 did not proceed. Even a fragment removed from 

 the same side (the left) of the larva displayed a like 

 infolding, so that a single larva might thus be induced 

 to form three sacs. These results show that in this 

 case the laying down of an organ does not, as Driesch 

 has supposed, limit the faculty of the remaining cells 

 to form a corresponding organ, or perhaps one 

 should say "of the neighbouring cells," for fragments, 

 removed from the right side of the larva produce, not 

 an echinoid sac, but an infolding that seems to repre- 

 sent the formation of a new larval gut. In larvae 

 from which the echinoid rudiment has been removed 

 further deviations from the normal process occur 

 and resemble changes observed in some abnormal 

 holothurian larvae — an observation of much theoretical 

 importance. 



In recent years dried blood has appeared frequently 

 on the market as an animal food, and, consideriny 

 the large quantities of this material which are avail- 

 able daily from the abattoirs of Great Britain and 

 the increasing difficulties of obtaining nitrogenous 

 food for animals, an inquiry was started as to the 

 value and safety of utilising dried blood as a 

 nitrogen-supplving food. Blood collected in smalt 

 quantities and stored before drying is useful only 

 as a manure, but blood which is dried immediately 

 after collection may be used as animal food. Mr. 

 L. F. Newman, in the Journal of the Ministry of 

 Agriculture for June last, contributes the results of 

 some feeding experiments with dried blood. He con- 

 cludes that the addition of blood to an ordinary farm 

 ration of wheat offals may cause considerable gain 

 in weight compared with the results from a diet of 

 offals only, while the addition of blood to plain maize- 

 meal may give an increase equal to the results ob- 

 tained from feeding offals only. .Another material 

 which has been suggested as animal food is the 

 bracken rhizome, and a paper by Prof. James Hen- 

 drick on " Bracken Rhizomes and their Food Value " 

 appears in the Transactions of the Highland and 

 .Agricultural Society of Scotland (1919). Prof. Hendrick 

 carried out preliminary feeding experiments which 

 indicated that bracken rhizomes are not rich enough 

 in the more valuable food constituents to be of much 

 use for anything but maintenance purposes, and even 

 here their usefulness is limited because they are not 

 palatable to certain classes of stock. During the 

 last fortv or fifty years, however, considerable damage 



