474 Messrs. 8. G. Shattock and C. G. Seligmann. [July 15, 
After the breeding season, that is to say about the end of June, the vividly 
differentiated plumage of the drake gradually passes into the dusky summer 
or “eclipse” plumage which renders the drake remarkably like the female 
bird in the colour of its feathers; this “eclipse” should be complete by 
about the beginning of August, and after three weeks or a month the 
reverse change begins to be obvious, the bird gradually reassuming the 
typical male winter plumage. We did not limit our experiments to the 
injection of cortical extract into young birds, but we also experimented on 
birds approaching the “ eclipse,” and in “eclipse” plumage. The validity of our 
attempts, however, is marred by the fact that the injections invariably lead to 
a local necrosis of tissue, which, although it does not obviously affect the health 
or comfort of the bird, actually produces a delay in the appearance of the 
secondary sexual characters. The ideal experiment would doubtless be to 
inject young mammals with the extract from the cortex of adults of the 
same species; we have already explained why we were forced to employ 
birds in our experiments. The further departure from the ideal experiment 
occasioned by the substitution of an extract of mammalian cortex for that of 
the avian adrenal was necessary for the following reason:—In birds the 
cortex and medulla of the adrenal gland do not form well differentiated 
structures as in mammals, but strands of cortical and medullary cells are 
interwoven throughout the gland in such a way as to make it quite impossible 
to isolate one from the other. The glands used for preparing the cortical 
extract were at first procured from goats and used almost directly they were 
taken from the body, but later on sheep were substituted, and the glands 
were often kept upon ice for 12 hours before using them; we found no 
difference in the result. The extracts were prepared with extreme care in 
order to avoid the possibility of bacterial contamination; the glands with the 
surrounding fat in which they are embedded were removed from the animal 
immediately after death and received in a recently boiled, corked or stoppered 
bottle ; they were then taken to the laboratory and used at once, or the bottle 
was placed on ice until wanted. In either case the fat was removed from the 
glands with sterilised instruments and the gland immersed in 5 per cent. 
carbolic acid solution for 10 minutes; it was then washed in boiled salt 
solution and split into sectors with a sterile knife; the cortex was removed 
with sterilised curved scissors and the pieces washed in sterile salt solution 
and pounded with sterilised sand in a sterilised mortar. When the sand and 
pounded gland had formed a paste, a further quantity of sterile salt solution 
was added and the paste again treated by grinding and stirring. The 
brownish fluid obtained by this process was filtered into a sterile beaker 
through freshly boiled muslin, and the fluid so obtained was injected into the 
