

PIZZLE 



water, forming a five per cent, solution of pixol, and in 

 thi:> strength it is used for disinfecting linen and wash- 

 he hands. For the disinfection of dejecta a ten 

 per cent, solution is required. 



Pizzle rr,'-l) [ME.]. The penis, especially of a 

 domestic mammal. 



Placebo .-.":-. '-bo) [" I will please: " fut. of placere, 

 to please]. Anything prescribed for the purpose of 

 pleasing or humoring the whim of a patient rather 

 than for its therapeutic effect. 



^lacenta ( pla-sen' '-tah)[z. particular use of placenta, -?.a- 

 kovt, a cake: pl.,Placentie or Placentas']. In biology : 

 he organ of attachment of an embryo or fetus to the 

 wall of the uterus, and by means of which it is nour- 

 ished ; (/') the ovule-bearing portion of the ovary of a 

 plant. The mammalian placenta is a spongy mass of 

 tissue derived from the chorion and decidua, its evolu- 

 tion having begun with the differentiation of the ecto- 

 derm of the germinative area by the formation of a 

 thickened region called the area placentalis . It is a flat, 

 circular, spongy body, adherent during gestation to the 

 inner wall of the uterus and connected by the umbilical 

 cord to the fetus, and forming for it the organ of nutri- 



Himan Placental Villi. 

 Blood-vessels black. (From Stirling.) 



ion and respiration. The placenta is developed about 



he third month of embryonal life. The chorionic 



illi in contact with the decidua reflexa cease to grow, 



vhile at the decidua serotina the villi become exceed- 



igly numerous. The uterine mucous membrane in 



ihich the villi are embedded contributes a share to 



he formation of the placenta. This is known as the 



laternal, in contradistinction to the chorionic or fetal 



ortion. At term the placenta weighs one pound, is 



ne inch thick at its center, and seven inches in diam- 



ter. The fetal side is covered by the amnion and 



enetrated by the umbilical cord. The maternal 



irface is dark-red, irregular, and covered by the 



pper layers of cells of the decidua serotina. The 



lacenta is normally situated at the fundus, anteriorly 



r posteriorly. In the lower animals the placenta is 



>mewhat different. Of the Choriata, those possess- 



g a villous chorion, one class, including the horse, 



e pig, the camel, etc., presents the villi uniformly 



stributed ; there is no special accumulation anywhere. 



> the other class the villi are aggregated and specialized 



a particular region to form the placenta. Three 



.neties of placentae are generally described : (a) 



iat with numerous cotyledons (cow, deer, etc.); 



I zonal placenta (carnivora) ; (c) discoid placenta 



innkey, man). The zonal and the discoid placentae 



• deciduate. P., Adherent, abnormal adherence 



the placenta to the uterine wall after childbirth. 



, Allantoic, a placenta in which the chorion ac- 



1107 PLACENTA 



quires vessels by growing together with the vascular 

 walls of the allantoic vesicle {(Jngulata), as distin- 

 guished from a. chorionic placenta, q. v. P., Annular, 

 a placenta extending around the interior of the uterus 

 in the form of a belt. P., Battledore, one in which 

 the insertion of the cord is at the margin of the pla- 

 centa. P., Bell-shaped, one in which there is a par- 

 tial persistence of the chorionic villi in the upper portion 

 of the chorion. P. biloba, P. bipartita. See Placenta 

 duplex. P., Chorionic, a placenta in which the chorion 

 has its own vessels ( Unguiculata). It is regarded as the 

 most primitive type, as distinguished from an allantoic 

 placenta. P. cirsoides, one in which the umbilical 

 vessels have a cirsoid arrangement. P., Cordiform, a 

 heart-shaped placenta. P., Cotyledonary, P., Coty- 

 ledonous, a placenta the villi of which are collected into 

 groups ; this variety is confined to the Pecora. In the 

 giraffe, the placenta is partly diffused and partly coty- 

 ledonous. The Bovidiz possess a large number of 

 cotyledons ( polycotyledonous) , while the Cen-idce have 

 only a few. P., Deciduate, a placenta in which the 

 fetal villi are so intimately connected with the uterine 

 wall, that at birth a greater or less portion is brought 

 away with the allantois (after-birth). It occurs in all 

 those Eutheria not included among those mentioned 

 as having non-deciduate placentas. P., Diffused, a 

 placenta which extends over the whole of the chorion. 

 It is characteristic of the Perissodactyla , the Suina, the 

 Tragulina, the Tylopoda, the Sirenia, the Cetacea. and 

 the Lemnroidea. P., Discoid, a placenta which is 

 disc-shaped. It occurs in the Rodentia, Insectivora, 

 Chiroptera, and the Loricata among the Edentata. 

 The discoid chorionic placenta is regarded as the 

 most primitive type, as distinguished from the zonary 

 placenta of carnivora, the diffuse placenta of the lower 

 primates, and the metadiscoid placenta of man, which 

 have been evolved from it. P., Disseminated, one 

 in which the cotyledons are not distinctly localized 

 to one area, but are scattered. P., Dome-like. Syn- 

 onym of P., Bell-shaped. P., Double. Synonym of 

 P. duplex. P. duplex, Placenta biparlita ; an 

 anomaly of the placenta, in which it is divided into 

 two portions. P. evanida, the placenta of a blighted 

 ovum in which all structure has been lost from pressure 

 by the surviving ovum, as is seen in some cases of 

 foetus papyraceus. P. fenestrata, one in which the 

 true placental tissue is lacking in one or more places, and 

 the chorion, being free from villi, forms a transparent 

 membrane. P. fcetalis, the smooth amniotic surface 

 of the placenta. P., Fundal, one attached at the 

 fundus. P., Horse-shoe, in twin pregnancy, a con- 

 dition in which the two placentse are united by a strip 

 of placental tissue. P., Hydatigenous, a placenta the 

 seat of myxomatous degeneration, as in hydatidiform 

 mole. P., Incarcerated, a placenta retained in the 

 uterus on account of irregular contraction of that 

 organ. P., Lateral, one attached to the lateral wall 

 of the uterus. P. marginata, an anomaly of the pla- 

 centa in which that organ is surrounded by a margin 

 or collar of placental tissue. P., Maternal, the por- 

 tion of the placenta contributed by the part of the 

 mucous membrane of the uterus known as the decidua 

 serotina. At birth the maternal portion is only a thin, 

 grayish layer on the uterine surface of the placenta, and 

 can only be stripped off in small pieces. P. mem- 

 branacea ; occasionally there is a failure of the atrophy 

 of a portion of the chorion which normally occurs, and, 

 instead, placental villi are developed over the entire 

 surface of the chorion. Such a placenta is called 

 placenta membranacea , and is thinner than the normal 

 placenta. P., Metadiscoid, P., Secondary Dis- 

 coid, a form of placenta found in the Anthropoidea. 



