Physiology. — “Concerning the Influence of the Adrenal Cortex 
upon the Growth and the Reproduction of Lower Organisms 
and its presumable Antitoric Action’. By Miss M. A. vaN 
HeRWERDEN. (Communicated by Prof. C. A. PEKELHARING). 
(Communicated at the meeting of March 26, 1921). 
I have been studying the influence of various tissue-extracts on 
the cyclic reproduction in a race of Daphnia pulex bred for many 
years in the laboratory. I thereby hit upon a phenomenon which 
led me to make further experiments. Although these experiments 
are still in progress, I consider it worth while to say a few words 
about this problem here, as it is one of general importance. 
The first time when I added a small quantity of dried adrenal 
cortex from the ox to my Cladocera cultures, it appeared to produce 
a peculiar effect. First of all the fecundity of parthenogenetic females 
is considerably intensified, sexual maturity commences sooner than 
in the control-animals (for which I always selected sisters from one 
and the same brood) and the generations follow each other in quicker 
succession. Not infrequently as many as three broods have been 
deposited, while the control-sisters are still bearing their first. It also 
often bappens that the first generations have reached maturity while 
the ovary of the untreated sisters is still infantile. This great difference 
may be seen as well when the control-culture contains only ditch- 
water with unicellular algae, as when for purposes of comparison 
an equal quantity of adrenal medulla was added insteadof cortex. 
Furthermore there is another very remarkable influence of the 
adrenal cortex upon the cultures, which is not exerted by the medulla. 
It is to this phenomenon that I wish to call special attention. It is 
well-known that Daphniae do not tolerate multicellular algae in the 
culture-glasses. The presence of these long filaments invariably 
occasion in my cultures depression, and ultimately induce death, if 
the animals are not transmitted in time to fresh ditch-water with 
unicellular algae. It now appeared that the addition of a small 
quantum of dried adrenal cortex, or an aqueous extract of it, was 
sufficient to ensure a healthy life to the Daphniae in a tangle of 
