z 7 6 



THE QUARTERLY REVIEW OF BIOLOGY 



If the mortality chargeable to the ali- 

 mentary tract and its associated organs is 

 examined in detail there is again seen to 

 be a regular progression associated with 

 advancing phylogenetic position. The 

 proportionate mortality from diseases 

 finding their seat in the alimentary tract 

 and its associated organs is highest in the 

 reptiles., lower in the birds, lower still in 

 the mammals, and finally lowest in man 

 living under superior conditions of present- 

 day civilization (England and Wales). 

 A human society less highly developed 

 from the viewpoint of public health and 

 hygiene (Sao Paulo) has a relative ali- 

 mentary tract mortality identical with 

 that of the mammals other than man. 



There is another point which needs 

 consideration in connection with the 

 mortality charged against the alimentary 

 tract. The figures of the last two columns 

 of table z, relating to man, are based upon 

 deaths at all ages, including infant mor- 

 tality. But in human infants, as I showed 

 in table n of The Biology of Death (9, 

 p. 136), it is the alimentary tract which is 

 concerned in the largest proportion of 

 fatalities, the percentage being 68.8 in the 

 case of males and 40.6 in the case of fe- 

 males. In the figures of table z above 

 relating to the lower forms, reptiles,, birds, 

 and mammals, there are included pre- 

 sumably very few if any deaths of ex- 

 tremely young animals. It is a not 

 unreasonable inference that if "infant 

 mortality' ' were included in the figures for 

 animals the proportionate mortality 

 chargeable to the alimentary tract would 

 be even higher in reptiles, birds, and 

 mammals than the figures actually avail- 

 able indicate. 



There is a regular progression of in- 

 creasing mortality chargeable to the 

 nervous system as we go up the evolution- 

 ary scale, and the same thing appears to 

 be true for the excretory organs, with some 



minor fluctuations in the figures not 

 greater than might reasonably be expected 

 by chance, where the numbers involved 

 are so small. The tendency to increasing 

 mortality from breakdown of the nervous 

 system was long ago noted by Laycock (3) 

 in his lectures on constitution in relation 

 to disease. He said (p. zo6): "Man as 

 compared with other animals is peculiarly 

 predisposed to degeneration of the nervous 

 system; and civilized man, as compared 

 with uncivilized." 



Up to this point in the discussion the 

 assumption has been that the deaths which 

 failed of autopsy could be regarded as a 

 fair random sample of all deaths, in 

 respect of their pathology. But table 1 

 shows that the proportion of such un- 

 autopsied deaths to all deaths is much 

 higher in the Zoological Garden experi- 

 ence than is the proportion of human 

 deaths falling in our Class X to all human 

 deaths. While the assumption made as to 

 the random distribution pathologically of 

 these undistributable deaths seems prob- 

 able a priori, there is no way to demon- 

 strate it directly. It is, however, possible 

 to get some indirect evidence which will 

 help towards the estimation of the extreme 

 possible error which would be made if this 

 assumption were wholly wrong. 



The most marked evolutionary trend in 

 table z is seen in the mortality charged 

 against the alimentary tract and its 

 associated organs. Now suppose we 

 make the two possible assumptions which 

 will set the extreme limits of the effect 

 which could be produced by altering the 

 distribution of the organologically un- 

 assignable deaths of Class X. 



I. The first of these assumptions is that 



All X = VI, 



that is, that all the deaths now in Class X 

 were in fact due to breakdown of the ali- 

 mentary tract and its associated organs. 



