228 'rinrh/si.rll, Amnnil Mrr/im 



l.iin life for (liiys; hut if the supply of ow.i^vii is >lnil oil', life 

 can 111' (•(intiiiuid duly Inr a \ryy few niiuulc- nu the slock oi' 

 <i\yi:-cn contained in the hody. So nai-|-ow i> the space hetweeu 

 aiiuudauce of o.\y<i-eu and death fi-oui oxyi^vu stai'\ at ion. In a 

 c<jld-hluu(!ed aniiual — with which the lake ou.ulit to he coiupai-ed 

 — processes of |-espii'at iou a I'e slower hut the i-elati\c situation is 

 not inatorially .lilTeivut. The j'esult of these conditions is thai 

 in any lai-,i;v animal enoianous surfaces must he [M'oxideil I'oi- the 

 al)Sor})tion of oxyizvii and there must In- a perfect mechainsm foi- 

 its (listri hilt ion. Such respiratory system.- exi'^l in a uicat 

 variety of forms, many of which are extremely complex and 

 etlicient. In the t-ase of man the ahsorhinu- surface of the lun-s 

 is said to amount to ahout two thousand s(|ua!-e te:'t — an area as 

 great as the condiined surface of lloors. walls, and ceiling;- of a 

 room 20 fVot srpiare and 1.") feet hi^h. The necessity for arraiit^'e- 

 monts for a laruc ahsorhiuu' surface increases with the size of the 

 animal, since in a lai'u'e or,u-anisin the area of the general siirfac:: 

 is far smaller in proportion to its mass than in a small orpinism 

 (d' the same shape, in a lake, whose size is enormous as com- 

 l)ared with that of any livin.i;- hein,i;-, the ahsorhini;- surface is 

 \-ery small as conii»arcd with its mass: hciua- only the up|)er sur- 

 face of the water. The lake is, thend'oiv, at a '^vv.W disadvama.uv 

 in the nuittei' of ahsorhin.y' oxy.ucn as com])arcd with the animal. 

 Still further, all hi-iier animals, holli cold-hloodcd and warm- 

 l)looded. contain in tlieir hlood some chemical suhstance which 

 lias a spi'cial allinity for oxyu'eii and which can I'apidlx' pick up 

 lariic (|uanlilies (d' it. Such a suhstance i> wholly lacking- in 

 the water of the lake, whose respiratory power is cori'cspondin.ii'ly 

 smalu'T. hoth as re_i;'ards the rapidity with which oxy^ucn can he 

 taki'ii u]) and the amount which can he ahsorhed. It is iiide-d 

 true that water will ahsorh, accordin,>:- to llu' ,uvncral laws of the 

 absorption of i^-ases, ahout twici' ;is much oxy.i:en as nitroLi'en 

 U!i(h"r similar conditions. This fact allows the lake to take in a 

 laru'cr stoidc of oxyu'en than would otherwise h- itossihie. and ihat 

 part of the atmosphci'e wliicli is dissohed in the lake contains 

 ahout oiie-third oxv-vn instead of one-lifth. as is ihe case out- 

 side. l>ul excn ihis amount is \ery I'ttle in comparison to the 

 cnonuous volumes which a suhstance like haemoiiiohin can take 

 up. It is also triu" that tlu' mass of the water of the laki', in 



