484 



SCIENCE 



[N. S. Vol. XXV. No. 639 



structures themselves; but they are pro- 

 vided, nevertheless, vi^ith some such factors 

 by their connections with other tissues. 

 The bones and cartilages, on the other 

 hand, which are but little influenced by 

 other tissues, are provided with a very large 

 margin of safety over the stresses to which 

 they might be exposed normally. Triepel 

 here makes a remark which has a direct 

 bearing upon the problem with which we 

 are dealing. He says that the large sur- 

 plus of material in bone and cartilage 

 shows that nature does not follow the law 

 of obtaining a result by the smallest pos- 

 sible means. 



It is worth noticing that the terge margin 

 provided here can not have the object of 

 offering protection against unexpected con- 

 tingencies coming from within the body, as 

 these, according to Triepel, will never reach 

 even the yield-point of these tissues. The 

 protection is here provided against con- 

 tingencies coming from without, against 

 injuries of external origin. It is a protec- 

 tion not against an internal, a physiolog- 

 ical, calamity, but against an external, so 

 to say pathological, contingency. 



A sufficient number of readily available 

 data for the study of our problem we find 

 in researches upon complex tissues or or- 

 gans. "We shall begin with the bilateral 

 mechanisms. Here are, in the first place, 

 the kidneys. Every medical man knows 

 now that one kidney can be removed with 

 entire impunity, if the other kidney is nor- 

 mal. The amount and the composition of 

 the urinary secretion remains practically 

 unaltered and this even soon after the re- 

 moval of the kidney. That can only mean 

 that normally the kidney has an abundance 

 of tissue which can do at a moment's notice 

 at least twice the normal amount of work. 

 From the experimental work of Tuffier, 

 Bradford and others we know that at least 

 two thirds of both kidneys may be removed 



without serious detriment to the animal's 

 life and to the secretory function of the 

 kidneys. At the same time we must re- 

 member that the normal secretion repre- 

 sents by no means the minimum amount of 

 work of the kidney. We know that the 

 average quantity of the urine as well as the 

 normal quantities of its various constitu- 

 ents may be greatly reduced without any 

 visible detriment. In fact there may be 

 anuria for many days without any serious 

 symptoms and perhaps also without serious 

 consequences, if the anuria be not due to a 

 disease of the kidney, but to such causes as 

 hysteria, calculus, reflex, or compression. 

 The margin of safety in the tissue of this 

 eliminating organ amounts at least to twice 

 its normal need. 



This would seem to be an unreasonable 

 luxury, a waste. But what a blessing. For 

 a score of years, 'or more, in many of us 

 the kidney is gradually losing some of its 

 valuable material from one cause or an- 

 other without any symptom, without a re- 

 minder sufficient to spoil our pleasure of 

 life or to hamper our activities. Not until 

 that luxurious surplus is approaching its 

 exhaustion, do we get a warning. But then 

 our work is mostly done and our time limit 

 nearly reached. 



Next we shall consider the lungs, an 

 organ of supply and elimination of first 

 order. We all know that life may con- 

 tinue though a great part of the lungs be 

 destroyed, if only the disease which caused 

 the destruction come to a standstill. We 

 know that in some cases of pneumonia one 

 lung can be entirely consolidated without 

 seriously impairing the process of ventila- 

 tion. Furthermore, a patient whose thorax 

 was freely opened to evacuate a one-sided 

 pleural abscess has after the opening less 

 dyspnoea than before. In empyema as in 

 pneumonia, it is essentially the infection 

 and intoxication with their reactions which 



