84 
ORGANIC DEPENDENCE AND DISEASE 
tivities, an unsolved problem. This activity of course plays 
a large part in the scavenging process which helps to clean 
up the organic excesses 
and restore the inor- 
ganic balance of nature. 
If algae can cause the 
deposition or secretion 
of lime carbonate, as 
they began to do on a 
vast scale even in Pre- 
cambrian times, and do 
this in effect by extract- 
ing the excess molecule 
of carbon dioxide from 
waters carrying lime 
carbonate in solution, 
it seems reasonable to 
a believe that in the same 
early ages algae might 
also have been the in- 
struments of lime solu- 
tion by virtue of the 
excessive atmosphere of 
carbon dioxide which 
they of necessity car- 
ried about them. Gener- 
ally estimated we must 
ascribe to these plant 
parasites an early adap- 
tation and an increas- 
ing activitv which seems 
to be in fair correspond- 
ence with the increase 
in lime-slielled inverte- 
brates. Unknown hith- 
b 
Fig. 68. Perforating algae Hayesia hematitica 
in the shell of the brachiopod Lingula. From 
the iron beds of the Wabana series (Ordovi- 
cian). Conception Bay, Newfoundland. 
a. x 110. b. x 100. (A. O. Hayes, op. cit.) 
