GENERAL DISEASES 171 
action of the contained sulphur on certain metallic salts which the 
fowl may ingest and which through metabolism may be incorporated 
into a yolk. 
There is no apparent reason why eggs so affected should be un- 
wholesome. They may be detected by candling. 
DOUBLE YOLKED EGGS 
The inclusion of two yolks within one shell is due to rapid 
ovulation or delay of one yolk in its progress to the isthmus or egg 
membrane-secreting part of the oviduct, thus allowing the following 
yolk to reach it and be surrounded by a common membrane. When 
the two yolks do not meet until arrival at the isthmus, each is sur- 
rounded by a separate layer of albumin. When two yolks are ovu- 
lated within a short interval or meet in the anterior portion of the 
oviduct they may have a common layer of albumin and common 
membranes. 
SOFT SHELLED EGGS 
When the egg reaches the uterine portion of the oviduct under 
normal conditions the double membrane secreted by the isthmus 
is covered by a felty fibrous layer into which is deposited the ma- 
terial which forms the calcareous shell. Absence of the hard shell 
may be due to several causes. If the bird does not have feed con- 
taining lime salts in sufficient quantity, or access to, substances rich 
in these salts it is apparent that a normal shell cannot be produced. 
Providing the fowls with crushed oyster shells or mortar will remedy 
this defect. Irritation of the oviduct as a result of inflammation 
may cause an abortion of the egg before it is properly formed. 
Sudden fright may also lead to a premature laying of the egg before 
it has acquired its hard shell. Excessive attention by the male is 
said to cause the laying of soft-shelled eggs. Where this is con- 
sidered as the cause the removal of the cock is indicated. Except 
when eggs are desired for incubation the presence of a male bird in 
the flock is not necessary since fowls lay equally well or better in his 
absence. Unfertilized eggs keep better than fertilized ones, a fact 
which causes many poultry men to place cock birds in the flock 
during the breeding season enly. 
