'J'liii li/-sl.rlli Aniiuiil M eel I lit/ 



and siinilai' liodics of watci'. Such lakes may sii|i|i(>fl an aliun 

 (lant ]M)|)nlalinn (if lisli liotli in ilic wai'nici- and the cdolci- water. 

 If they (1(1 iKil (1(1 so. llie faull does not lie willi tlie oxv-^'eii 

 supply. 



'Iduis we see lliat if we desii-e lo detei'Uiine llie capacity of a 

 lake I'oi- tile do\('lopineiil of hi_i;iiei' life, we must consider not 

 only its capacity (dv food pi-oduclion hut also its respiratory con- 

 ditions. !t may he that an imperfect inspiratory mechanism 

 renders a xcry larn'e share of the ])ottom of the lake wholly un- 

 iidiahitahle \'nv aninuil life: that while, foi- instance, mud-livin^i;' 

 inscci lar\ae may he found in the mud ai'ound the lake to a 

 dei)th of twenty or thirty feet, they are excluded hy the ahsence 

 of oxyux'u from the entire hottom of the lake lieyond this depth, 

 an area of ])erhaps many square miles. 'Fhc supply of food 

 which the lake oifers to the hio-her animals may thus he i^ivatiy 

 limited hy the la(d< of oxy^-en. It may he ti'ue also that the 

 oTeater ])art of the \olume of the water of the lake is un;n- 

 hahitahle foi' similar reasons, and that a lake whose surface ap- 

 pearance would indicate that it is t'a]>ahle of sup|M)i-tin,i:' enor- 

 mous (plant ities of fish life may he wvy considerahly restricted 

 in this resi)eet hy its res])h'atory ca|)acity. Kaeh lake should he 

 studied lioth as to food and oxy,i>t'n if an intelli.iivnt economic 

 use is to he made of its waters: and when this is done, the possi- 

 hilities of use will often he found to (lei»end on the re<p:rat(U-y 

 mechanism. 



I have said nothin.u' on anothei- side of the methods of ah- 

 soi.'hiiii:- and 1 i-ans]i(n'tini:- pises in a lake. The same processes 

 which take ow,L;eii from the surface lirinu' waste ji'ases to it and 

 thev are as ellicient or as incHicient 'n the latter ]irocess as in 

 the foi-mer. Processes of ahsorptioii and t I'ansportation have 

 much to do with the story of the complex i-elatioiis of carhon 

 dioxide .^as in the lake. These matters. howe\-er. can lietter he 

 spoken of under internal !-es]»irat ion. 1 need only say here that 

 the accumulation of waste leases in the lowei- water doi-s not sivni 

 to all'ect life unfa\(irahl\- if tliei'e 's pk'uty of oxy^u'en present 

 •also. Kespiratory inetlicieiicy limits life in a lake hecause of 

 lack of oxy.iicn rathei- than hecause it allows poisonous u';ises to 

 collrct ill lai-.i^-e (piaiilities. 



'Idle suhjet't (d' iiitei'iial respiration deals with the changes 



