10 
Transactions Texas Academy of Science. — 1907. 
(probably bicarbonate soda), which neutralizes the acid chyme, which 
neutralization is a signal for the apening of the pylorus and the 
passage of still more chyme into the intestine, after which the process 
commences afresh. 
The study of these “hormones,” or chemical messengers, is a par- 
ticularly interesting one; especially so as it has completely annihilated 
the school of nervous physiology. 
Much interesting work has been done in this direction, and at a time 
when we are so concerned over the physiological effects of animal ex- 
tracts and antitoxins, it might be wise to mention other important 
observations on the subject. 
It has been found that the enlargement of the breasts which occurs 
during pregnancy is due to a hormone secreted by the foetus. It has 
long been known that if abortion occurs in the early stages of preg- 
nancy, the breasts return to their normal condition, without milk being 
formed; whereas, if the foetus is removed in the later stages, lactation 
occurs just as if labor at term had resulted. Previously it had been 
recognized that nervous influence was not responsible for lactation, 
because the spinal cord in pregnant bitches could be divided without 
interfering with lactation; furthermore, in some clinical cases of com- 
plete crushing of the spinal cord in pregnant women, lactation occurred 
after labor just as usual. Therefore, the possibility of a hormone being 
the cause was considered. Starling cleared this matter up by finding 
that he could produce a stimulation of mammary secretion in virgin 
rabbits by injecting an extract obtained from the bodies of foetal rabbits. 
Again, it has been found that testicular secretion is absolutely neces- 
sary for the production of male characteristics. If the vasa deferentia 
are divided and the testicles left in place, male characteristics are still 
developed although the procreative power is destroyed. But on 
the other hand, where castration is performed in early life, the in- 
dividual never develops male peculiarities, as revealed by the high- 
pitched voice and the scanty growth of hair on the face. In animals, 
as Shattuck and Seeligman have shown, the results of experimentation 
are remarkable. In sheep and fowls double castration resulted in the 
non-appearance of the male characteristics, viz., the growth of horn 
and spurs; while double vasotomy (the testicles not being interfered 
with) did not effect the growth of these particular male appendages. 
Further, in cases where the testicles were removed, the growth of male 
features could be secured by the grafting of testicular tissue into the 
abdomen (Abrahams). 
Another interesting line of experiment has been opened up in find- 
ing that the corpus luteum is responsible for the proper fixation of the 
impregnated ovum to the uterine walls. It has been found that, if an 
