882 PHYSIOLOGY OF DIGESTION AND SECRETION. 



prepared commercially under such names as pituitrin, infundin, 

 hypophysin, etc., but the active principles or hormones assumed 

 to be secreted have not been isolated in such forms as to admit 

 of a determination of their chemical nature. In the posterior lobe 

 it is stated that in addition to the pressor substance responsible 

 for the increase in blood-pressure and for the oxytocic activity 

 there may be present, especially in extracts of the dried glands, 

 small amounts of histamine and a histamine-like substance, f It is 

 doubtful whether such substances exist in the normal gland, but 

 their formation in the dry product may explain the fall in blood- 

 pressure sometimes observed as one phase of the reaction pro- 

 duced by the injection of extracts of the posterior lobe. 



The Pineal Body (Epiphysis Cerebri). — This small body 

 projects from the roof of the third ventricle and embryologically 

 develops as an outgrowth from this vesicle of the brain. In early 

 life it has a glandular structure which seems to reach its greatest 

 development at about the seventh year. After this period and 

 particularly after puberty it undergoes a process of involution 

 during which the glandular structure gradually disappears and its 

 place is taken by fibrous tissue. The gland is noteworthy also for 

 the appearance of calcareous concretions, the so-called brain sand, 

 which may appear even in early life. Intravenous injections of ex- 

 tracts of this gland seem to cause a distinct fall in blood-pressure, 

 indicating the presence of a depressor substance. On the patho- 

 logical side it is stated that in young children invasion of the gland 

 by pathological growths results in distinctive effects. Under such 

 conditions there is presumably a diminished activity of the gland, 

 and the results observed are an accelerated development of the 

 reproductive organs, with an attending mental precocity and an 

 increased growth of the skeleton. The inference made, therefore, 

 from these observations is that in the young child the gland fur- 

 nishes a secretion which inhibits growth and particularly restrains 

 the development of the reproductive glands, but it should be 

 noted that this conclusion is not well supported by experunental 

 evidence. Total extirpation of the gland gives no decisive effect 

 upon dogs (Dandy). On guinea-pigs it is stated (Horrax) that 

 pinealectomy causes an accelerated development of the sexual 

 organs in the male. 



Organs of Reproduction. — Some of the earliest work upon the 

 effect of the internal secretions of the glands was done upon the 

 reproductive glands, especially the testis, by Brown-Sequard.f 

 According to this observer, extracts of the fresh testis when in- 

 jected under the skin or into the blood may have a remarkable 



* Abel and Nagayama, "Journal of Pharm. and Exp. Ther.," 15, 347, 1920 

 t "Archives de physiologie normale et pathologique," 1889-92. 



