A III cried II Fl.^li cries Soeicfi/ 23o 



of pises within the l;il<(' itscll' ;iii(l with tlu' inamifiU-turc of unses 

 l)y \\\v orii-auisiiis wliic-li 'iihahit it. Xo lii-aiich of pliysiolo.u-v is 

 more iiiti-ic-alo and none loss understood than is tliat of internal 

 res])ii'ation. This is tnu' also of the internal resi)iraiioii of the 

 lalve'. Tile ,y'aseous e.\ehaii,u'es and the niamifacturiiiii- opi-rations 

 ill the interior of a lake are far more (-((niplex than those of any 

 animal. From the water liv'no- heiiigs are drawing- su|)])lies of 

 ii'as. eaeli after its kimh and to the water each is eontriliutin^u- 

 ^ii'ases ditferin^L;' in amouni and eomposition. Animals are witli- 

 drawin.ii,' oxy^iieii from the waler ;ind i;i\'nu- earhoii dioxide to it. 

 Algae are rei)eating this pi-ocess hy iii^ht and exactly revt'rsin,"; 

 it hy day. Finiiii and hacteria are usin,^' oxy^u'en in the course of 

 their internal \ital aeti\it'es: they are t'luployinu- far lar«'er 

 (|uantities in the fenuenlat i\'e ])rocesses which thev maintain. 

 The numhei'less cli(niical elian_ii'es included iimU'r (lec(>m]tosi- 

 tion and fi'rmentat on, ,ii<»iiiii' <>ii nnder all sorts of conditions, 

 iuvolvin<i- numerous kinds of materials, and operated hy various 

 ora-anisms, are addin,i;- to the water ,ii-ases of different kinds and 

 in \aryiii,L;' pi'oportions. The upper water, the lower water, and 

 the mud pi'eseiit \-ery dissimilar lields of woi'k to the organ'sms 

 which inludiil them. It is. therefore, impossihie even to attempt 

 a ])ictiire of the int<'rnal I'espii'ation. with the innumerahle opera- 

 tions, eacli add'ni;- to or suhtracliii,u' from the sum of ,ii'ases .in 

 llie lake; in an intricate network of processes, consecuti\'e. cor- 

 relative, and antagonistic; t'oniiectt'd hy ndations which cros^ 

 and interlock at a thousand i)oiiits. I shall speak of only a few- 

 detached topics. 



I have said that the oxyu-eii of the lake is ahsorlted from the 

 air. This is true so far as the main stock of oxyyi'ii is con- 

 cerned ; hut a lake lias a second source of oxyyen which is always 

 considerahle and which in certain places and relations may he- 

 come ini])ortant. The ,y-reen ])lants which inhal)ii the lake are 

 alile to take up carlion dioxide from the -watei', and under the 

 influence of li^-lit they can use it in the manufacture of starch. 

 s(ttin,u' oxy,u'('n free in the i)rocess. In lakes which contain an 

 ahundance of al.uae. considerahle ([uautities of oxyg-en may arise 

 fi'om this source and this manufactured oxygen may play an im- 

 portant part in the vital h'story of the lake. 



Consider the etfect of the addition of this i)ower of the algae 



