STUDIES ON THE PHYSIOLOGICAL CHARACTERS 
OF SPECIES 
I. THE” EFFECTS OF CARBON DIOXIDE ON VARIOUS PROTOZOA 
MERKEL HENRY JACOBS 
From the Zoédlogical Laboratory, University of Pennsylvania 
CONTENTS 
Jeo dG alr eXOXe ROVGRBICOY Mts eo o'r & God Be. 8 oes rc GN Ceerteev ne ten AIel RO SaIRAIR SIE eI lars alk Pats 519 
ieee tentalkamcumethh Od skrgess rs ere ls ot ns oo Ra hace 521 
i Observavionstancexpenimacibspeseeccs oat atic eee cree 524 
Nes (ONIN FOI ses cts vs ychc te ace pe RENT 5 cca ase eo ee Ries 524 
ieeRaraneciumatesuda tums... eee Paes is ote 8 1 pe be eee 524 
Demi aman e@iimara unre ae. ay. aa eae ete aan ohne ae ii ae Se TE 
Bs Lee CMIOMOUNESIN es con bogagooboscsoauacanacedcoctaecodune GOS 
Aa Coloraiumicolpod assert; eee ee ee 529 
em COLE SMITH USUA ee sheis crs ne hte eee ee Cn ee eet ene 530 
Geo lepnanism a Materia~ cca haces one oes Seles ero eae 530 
DUNT OGES Abe LAs. =< acs ev sae mete Oe ee oa Re eee OS 
Sonuicellasne bulifterd:sa- sc eee ements at oe 
Bact lagelllatestppe vars cts 2 4d). as cn ae ey a umn Oe Be oe 2h 534 
IR VP ecraneniagtrichophorum: >see erate eer eee rire aoe 534 
Pee Died eine) AADAOD SE GO Mee epee tisioc c,. 4 6a nclcs Metso Soe an Den S.« 535 
Se Chilomonasyoanralnc Cina. eee ee eee eis ee 536 
Ms ean AE OSI 0 MONO SIN CEH LUO Ge ee cOt) rte ae Si naan actaeh AES es 537 
IVA DIScusstonyolmesulitsamaeertsr. ccs. isn he ace eee Rae Rete aS ie Se Ie7/ 
Wig TUOMAS cee Get occsb5 6) dhe Grae eae SA ret A ae seen iNet A 540 
Feast Wea Tp EATS Ah 5s oye shy EMS atest «ox lan af Oe ae eet ally ARR AS one cl bce 541 
I. INTRODUCTION 
Considering its importance in connection with many aspects 
of modern biological research, the question of the physiological 
characters of species, as opposed to their morphological ones, 
has received a surprisingly small amount of attention. This con- 
dition has doubtless resulted partly from the fact that physio- 
logical characters, on account of their less definite and tangible 
519 
