336 



NATURE 



[May 20, 1909 



percentage increase of weight after birth occurs in 

 those animals which are born least mature. Thus in 

 the guinea-pig, which is born in a relatively mature 

 state, the daily percentage increment of weight just 

 after birth is 5 per cent., while the rabbit, which is 

 born much less mature than the guinea-pig, daily adds 

 17 per cent, to its weight. In embryonic life, 

 cellular division and increase in weight are still more 

 marked, and Prof. Minot estimates that 98 per cent, 

 of the original growth power has been lost at birth, 

 and the power of growth becomes less and less as 

 age advances. 



Differentiation and rejuvenation of cells are next 

 considered. In the embryo the cells differ but little 

 from one another ; they do not display structural 

 differentiation, whereby it could be said from what 

 part of the embryonic body they were derived ; while 

 in the adult the microscopic characters of a cell 

 generally suffice to determine its place of origin. 

 Moreover, with the differentiation of cells with age, 

 the protoplasm increases in amount relative to the 

 nucleus. The conception is therefore reached that 

 the growth and differentiation of the protoplasm and 

 relative diminution of nuclear matter are the cause 

 of the loss of the power of growth. 



If cells suffer from old age as their protoplasm 

 increases and becomes differentiated, a general and 

 progressive process in the individual, there should be 

 some mechanism for rejuvenation ; this the author 

 regards as accomplished by the segmentation of the 

 ovum, during which process an increase of nuclear 

 matter takes place at the expense of the protoplasm. 

 The author believes that there is no satisfactory 

 evidence that the progeny of old cells (other than of 

 the ovum) can resume the primitive state and undergo 

 re-differentiation. In cases in which regeneration of 

 excised parts, &c., is effected in the individual, e.g. 

 in . planarians and ascidians, the regenerated part is 

 always the product of undifferentiated cells, and is not 

 derived by the growth of the old tissues. 



The usual method of rejuvenation adopted by 

 nature is by the separation of cells in the primitive 

 and undifferentiated condition, and their isolation as 

 the germ or sex cells. Age then represents the result 

 of a progressive cytomorphosis of which death is 

 the culmination. Longevity, the duration of life, 

 depends, therefore, upon the rate of cytomorphosis, 

 which varies much in different species, and perhaps 

 in different individuals of the same species. Whether 

 rejuvenation can be improved and senescence delayed 

 are questions to which the author gives no definite 

 answer, though he surmises that in the future it 

 may be possible to increase the activity of nuclei and 

 prolong the younger system of organisation. Death 

 he regards as acquired during the process of 

 evolution in consequence of cytomorphosis. As 

 organisation becomes higher and higher, the need for 

 differentiation becomes greater ; this involves the end, 

 and death is the price we have to pay for the differen- 

 tiation which exists in us, and to which we owe our 

 great array of faculties ! 



This, in brief, is the argument of Prof. Minot, 

 which is presented in an attractive form with many 

 NO. 2064, VOL. iiol 



appropriate illustrations, and we have perused this 

 work with considerable interest. Finally, a sugges- 

 tion of some importance is made. The author 

 develops the conception that not only physical but 

 also psychological development is most rapid in early 

 life, and progressively declines as age advances. He 

 suggests, therefore, that the tendency there is in 

 some quarters to postpone the period of learning is 

 wrong, and that as much use as possible should be 

 made of the early years of life. R. T. H. 



THE SONGS OF BIRDS. 

 Kioist mui ]'ogelgesang in ihren wechscUeitigen 

 Bcziehungen von naturwissenschaftlich-musikal- 

 ischen Standpitnkte heleuchtet. By Dr. B.. Hoff- 

 mann. Pp. ix+230. (Leipzig : Quelle und Meyer, 

 igo8.) Price 3.80 marks. 



THIS is the most interesting book on the songs 

 of birds that has appeared since the late Mr. 

 C. A. Witchell published his " Evolution of Bird- 

 song " in 1896, and it excels that work both in 

 soundness of judgment and in knowledge of music. 

 Its object, however, is not quite the same as that 

 of Mr. Witchell's volume (which does not seem to 

 have fallen into Dr. Hoffmann's hands); the latter 

 was an attempt to trace the development of song 

 fiom call- and alarm-notes, and also from imitation 

 of natural sounds, while Dr. Hoffmann's work mav 

 be described as an essay on the relation between the 

 music of birds and the music of art. 



For dealing with this subject the writer is evi- 

 dently well qualified ; he is clearly a close observer 

 of all sounds made by birds in their wild state, and 

 wisely abstains from making use of the music of 

 birds in captivity, and at the same time he is quite 

 at home in the subtleties of the musical art. The 

 result is that we have here no foolish attempt to 

 represent the music of birds on our musical scale, 

 except in a few cases where it is possible tn do so 

 as a means of illustrating certain points rather than 

 as an exact reproduction of .the notes of the singer. 

 For Dr. Hoffmann is well aware that the great 

 majority of singing birds do not use the intervals 

 of our scale, though he is right in claiming that a 

 few occasionally do so. So, too, in a very interesting 

 section on rhythm in song, he denies that it is to 

 be found in any sense in a great number of songs, 

 while rightly asserting that it is present in those 

 of certain species, such as quail, great tit (Kohlmeise), 

 wood-pigeon, and song-thrush. 



In another section (pp. 99-122) he asks the ques- 

 tion how the bird comes by a sense of rhythm, and, 

 rejecting Biicher's theory that rhythm in music can 

 be traced to the movements of the bodv, he is dis- 

 posed to think that in the case of birds it has its 

 origin in the action of the heart; but this is a 

 delicate question, for which the reader must be re- 

 ferred to the author's own statement of it. Dr. Hoff- 

 mann also discusses the question of " Metrik " in 

 bird-song, i.e. Can the strains sung by anv birds be 

 divided into feet or bars? On p. 84 foil, he maintains 

 that in the song of the nightingale, the most highly 



