594 



NA TURE 



[February 27, 1908 



One of the objections to the employment of photo- 

 graphy as a means of illustrating natural history 

 books' is that very frequently the animals are taken 

 in postures which do not display their leading char- 

 acteristics, and thus render the pictures more or less 

 completely useless for the purpose of specific identifi- 

 cation. The same thing applies in the matter of 

 characteristic attitudes and the nature of the habitat ; 

 and, in the case of birds, to the form of the nest ana 

 the appearance and growth stages of its occupants. 

 To remedy these shortcomings in the case of the 

 feathered denizens of British marshes has been the 

 main object of the authors of the charming little 

 volume standing third in our list. They have set 

 themselves the task of portraying marsh-birds in 

 positions and attitudes which will render the pictures 

 of real service to the scientific ornithologist ; and we 

 venture to think that the verdict of their readers will 

 be a pronouncement of unqualified success in this re- 

 spect. As a specially good example of their work 

 we may cite Miss Turner's photograph of a bearded 

 titmouse, showing the black face-marks of the cock 

 from which the species takes its name. This would not 

 print satisfactorily in the pages of Nature, but we 

 are able to give another illustration showing the bird 

 feeding its young. The book does not, however, 

 depend entirely on its illustrations, and even in such 

 a hackneved subject as the life-history of British birds, 

 the reader will find much of interest in the brightly 

 written biographies which accompany the plates. 



R. L. 



STUDIES IN NATIONAL DEGENERATION.' 



THE several aspects of study which the statistics 

 deal with in this memoir are chiefly parental 

 and fraternal heredity, the fertility of tuberculous 

 stocks, and the distribution of pulmonary tuberculosis 

 in tubercular families. Prof. Pearson's observations 

 are admittedly, from a numerical standpoint, wholly 

 insufficient, but if his deductions are thereby rendered 

 inconclusive, he has pointed the way and laid the 

 foundation for further study of an all-important 

 subject. 



Prof. Pearson discusses only pulmonary tuber- 

 culosis, that is, phthisis, or, as it is popularly termed, 

 consumption ; yet even with this limitation it is un- 

 comfortable reading that about lo per cent, of the 

 inhabitants of the British Isles are affected by pul- 

 monary tuberculosis. Unfortunately, other organs 

 besides the lungs become the seat of tuberculosis, and 

 their disorganisation is attended by as serious results 

 as when the lungs alone are considered. It may be 

 that tuberculosis of the lung is, from the point of 

 possible national deterioration, not the most deadly 

 form of the ailment. Tubercular diseases of the bones 

 of the joints, of the lymphatic system, and of several 

 of the organs other than the lungs, prevail to an 

 extent little appreciated as being of an equally deadh' 

 nature, with the more evident lesions in the lungs. 

 They all indicate a diathesis, and give rise to types 

 of infirmities well known to medical men. These evils 

 of tuberculosis, therefore, are much more widely 

 spread than pulmonary tuberculosis or consumption 

 would give us to understand, and being less manifest 

 to the public scrutinv are more insidious and more 

 apt to be neglected in the reckoning of tuberculous 

 disease generally. 



That heredity plays an important part in tuber- 

 culous disease is, in Prof. Pearson's opinion, un- 



1 Drapers' Company Pesearch Memoirs, TI. A First Study of the 

 Statistics of PulmoT.ary Tuberculosis. By Prof. Karl Pearson, F.R.S. 

 Pp. 26. (London : Dulau and Co., T907.) Price 3J. 



NO 2000, VOL. yy] 



doubted. Recent beliefs point rather to infection as 

 being the major element in rendering the disease so 

 prevalent, and it is noteworthy that Prof. Pearson in- 

 clines to the older belief of heredity. He finds that 

 tubercular lung trouble is chiefly prevalent amongst 

 those who inherit a predisposition, that is, a phthis- 

 ical or consumptive diathesis. It is impossible, how- 

 ever, owing to insufficient data, to assume that the 

 tendency to any disease is inherited in the same sense 

 as are physical and mental characteristics, but did 

 inheritance not explain the matter it is difficult to 

 understand how anyone escapes the disease, seeing 

 that, in urban districts especially, the tubercle germ 

 is so prevalent that " few individuals who lead a 

 moderately active life can escape an almost daily risk 

 of infection." 



Such being the case, the tubercle germ can thrive 

 best in the suitable soil to be met with in lung tissues 

 which are prepared by hereditary predisposition, or, in 

 some cases, by what may be termed accidentally 

 acquired predisposition in the lung tissues themselves, 

 by previous local lesions. That the predisposition to 

 the lung becoming the seat of tuberculous disease is 

 to be statistically ranged alongside well-established 

 inherited characteristics, such as physical and mental 

 traits are known to be, can only be proved by obtain- 

 ing complete histories of multitudes of families and 

 family stocks. This, however, is at present a long 

 way off being established, and until this gap is filled 

 any deductions we make at present can only be 

 speculative for the most part. 



The period of life during which tuberculosis is most 

 likely to show itself in the lungs is between the ages 

 of twenty and thirty. The mean age of onset in 

 men is set down at the twenty-ninth year, and in 

 women at the twenty-fifth year. The actual danger 

 zone cannot, however, he said to be passed until the 

 fortieth year, or perhaps the forty-third year, is passed. 



The observation that there is but an insignificant 

 difference between the time of onset of the disease 

 when some member of the household is the subject of 

 tuberculosis and when no member is thus afflicted is 

 rather against the infection theory pure and simple; 

 for with the constant possibility of infection in the 

 immediate environment, phthisis should, according to 

 infection beliefs, appear at an earlier age than 

 statistics seem to sho\v. 



.\fter discussing the part played by parental and 

 fraternal heredity, Prof. Pearson concludes that the 

 tuberculous diathesis is inherited in the same way 

 and with the same intensity as the physical characters 

 are inherited in man. 



Concerning the fertility of tuberculous stocks, Prof. 

 Pearson shows that the pathological conditions do not 

 tend to reduce fertility, but, on the other hand, that 

 such stocks appear to be quite as fertile, and, in all 

 probability are more fertile, than normal stocks of the 

 same class in the community at large. The fact, 

 however, that tuberculosis is a disease of 3'outh and 

 early middle life distinctly lowers the marriage rate 

 and limits the child-bearing period of such stocks, and 

 thus reduces the total number of offspring born to 

 tuberculous people ; there can be no doubt that by 

 the inbreeding of purely tuberculous persons the stock 

 would become in time extinct. 



The question of order of birth, that is, whether the 

 child belongs to the early or late portion of a given 

 tuberculous family, is of considerable interest. Are the 

 elder or the younger members of the family the more 

 liable to develop tuberculosis and to possess a tuber- 

 culous diathesis? The children of old people, of, say, a 

 man over sixty and a woman of forty-seven, are popu- 

 larly believed to be handicapped in the struggle for 

 life owing to inherited physical defects. There is no 



