14 
So far as the sterility of cows is concerned, Zschokke dis- 
cusses numerous conditions which generally disturb the 
regular estrum, or prevent pregnancy altogether. 
The heat can be intermittent or entirely absent, it can 
be too weak or too irregular, or else it can be persistent. 
The irregular or totally absent estrum has either causes 
of a more general nature, or is caused by lesions of the 
ovaries. The missing heat period can be caused through 
age. It is, however, known that a cow in England produced 
her twentyfifth calf in her twentyninth year. Other causes 
are the passing of the first few heatperiods, obesity and 
phlegmatic temper. Several fat cows were examined but no 
pathological changes of the ovaries could be found; however 
a too narrow cervix and an abundant amount of mucous dis- 
charge were noted. Zschokke concludes that in these cases 
the heat had been very mild and had passed by without 
being noticed. Asa last general cause he mentioned malnu- 
trition, due to a quantitative or qualitative misproportion in 
the feed. 
As ailments of the ovaries he names: (a) Fibrous tumors 
on the surface of the ovaries. He found such in 8% of 300 
examined ovaries, and most frequently in older cows, (b) 
Congenital deformities, where the ovaries are either entirely 
lacking or not enough developed. This was quite frequent in 
twins, where normal ovaries were found in only 70% of the 
heifer calves, (c) Chronic oophoritis, generally caused by 
tuberculosis, (d) Sklerosis of the ovaries, (e) different tu- 
mors, and (f) corpus luteum persistens. The yellow bodies 
do not atrophy if there is an abnormal content in the uterus. 
This may be a dead fetus, a retained placenta or a patholo- 
gical discharge of the uterus. Sometimes, however, the yel- 
low bodies are found without a corresponding abnormality 
in the uterus and then the feeding with malt, rye, corn or slop 
from sugar beets may be responsible. 
Very mild heat symptoms may be an individual charac- 
teristic or may be caused by the feeding, by a continuous 
