EVOLUTION AND MORTALITY 



173 



autopsy, for mammals, birds, and reptiles. 

 The remainder fell into Class X (cf. infra), 

 incapable of organological classification. 

 Individuals not autopsied are accounted 

 for under such rubrics as "Eaten by rats;" 

 "Decomposed;" "Not examined." Be- 

 sides these there is the rubric "Killed," 

 which includes those animals killed by 

 other animals. Those killed on order, 

 because of illness or for other reasons, are 

 distributed to causes according to the re- 

 sults of the autopsy examination. Other 

 rubrics are "Not diagnosed;" "Exposure." 

 The number of deaths under these and 

 other organologically unclassifiable ru- 

 brics, such as "Debility," is large in the 

 case of reptiles, less in birds, and much 

 smaller in the mammals. In dealing with 

 the material one is obliged to assume that 

 these deaths constitute in part a random 

 sample, in respect of pathological causa- 

 tion, of all deaths; or, in the case of purely 

 accidental deaths, are of entirely healthy 

 individuals. In the second of these alter- 

 natives the deaths obviously have no 

 place in a biological classification. They 

 simply do not come into the reckoning 

 here, any more than with human mortal- 

 ity. As to whether the other organologi- 

 cally unclassifiable deaths are a random 

 sample, pathologically speaking, of the 

 total it is impossible to determine defi- 

 nitely. It seems probable that they are 

 fairly so, for the reason that if one com- 

 pares the statistics of different zoological 

 gardens, in which the proportions of 

 unautopsied or unrecorded deaths vary 

 widely, it is found that the ratios between 

 the different ascertained causes among 

 the autopsied and recorded portion of the 

 dead population are fairly constant from 

 garden to garden. This could only hap- 

 pen, assuming honest and fairly careful 

 autopsy work, as we are entitled to, if 

 the unrecorded deaths approximated a 

 random sample of all deaths in respect 

 of their pathological characteristics. 



The organological classification of the 

 causes of death set up in (8-10) and 

 followed in this present study is as 

 follows : 



I. Circulatory system, blood, and blood- 

 forming organs. 

 II. Respiratory system. 



III. Primary and secondary sex organs. 



IV. Kidneys and related excretory organs. 

 V. Skeletal and muscular systems. 



VI. Alimentary tract and associated organs 



concerned in metabolism. 

 VII. Nervous system and sense organs. 

 VIII. Skin. 

 IX. Endocrinal system. 

 X. All other causes of death. 



TABLE 1 

 Deaths in London Zoological Garden, 1 920-1 9 2$ inclusive 





MAMMALS 



BIRDS 



REPTILES 



YEAR 















MX 



X 



I-IX 



X 



I-IX 



X 



I^ZO 



2-73 



63 



369 



103 



I48 



H3 



I^ZI 



169 



33 



391 



IXX 



163 



109 



Ij}2.Z 



2.61 



58 



434 



Ml 



119 



107 



13^3 



M* 



90 



443 



196 



I38 



*53 



Totals 



944 



MS> 



1,638 



567 



568 



482. 



The actual numbers of the 4,448 deaths 

 in the London Zoological Garden, here 

 dealt with, falling respectively into 

 Classes I-IX inclusive, and Class X, are 

 shown in table 1. 



ORGANOLOGICAL DISTRIBUTION OF DEATHS 



In table z the biologically classifiable 

 deaths in the four years experience (192.0- 

 19x3) of the London Zoological Garden 

 are tabulated according to organ systems, 

 on a percentage basis, the figures repre- 

 senting the number of deaths in each class 

 per hundred deaths from all causes (ex- 

 clusive of those falling in our Class X). 

 For comparison the last two columns give 

 corresponding figures for human beings. 

 The first of these columns is from the 

 mortality of the City of Sao Paulo, Brazil, 

 in 1917, and the second from that of 



