PINOCYTOSIS 



271 



PLACENTA 



hydroxide, just sufficient to dissolve 

 the precipitate, Distilled water 100 

 ml. Dip in aq. dest. for a few seconds, 

 without agitating. Reduce in 10% 

 formalin (Merck blue label), to which 

 4 drops of pyridine are added for each 

 10 ml., 1 miu. agitating gently. Wash 

 in aq. dest. Tone in yellow gold chlo- 

 ride (1 g. to 500 ml. aq. dest.) for a 

 few seconds to 1 min. Time should be 

 checked carefully. Fi.x in 5% hypo for 

 1 to 2 min. Wash and counterstain 

 lightlv with 1% erythrosin or safranin. 

 Dehydrate in 80%, 95% and absolute 

 alcohol. Clear in two changes of 

 xylene, mount in neutral Canada bal- 

 sam and cover with cover slips (see 

 Nassar, T. and Shanklin, W. M., Stain 

 Techn., 1950, 25, 35-38). 



Pinocytosis, a term introduced by Lewis 

 (W.H., Bull. Johns Hopkins Hosp., 1931, 

 49, 17-26) to indicate drinking by cells 

 as opposed to phagocytosis, or eating by 

 cells. It means (Lewis, W. H., Am. J. 

 Cancer, 1937, 29, 666-679) microscopi- 

 cally visible drinking, not submicro- 

 scopic "sipping" which Meltzer termed 

 "Potocytosis". By this process in tis- 

 sue cultures proteins and other sub- 

 stances that do not diffuse into the cells 

 are engulfed by wavy rufBe pseudo- 

 podia. The cell membrane, which first 

 invests the globulus of fluid taken into 

 the cytoplasm, later disappears and the 

 fluid becomes part of the cytoplasm. 

 Can be best seen in cultures of cancer 

 cells of which an excellent moving pic- 

 ture is available for distribution by the 

 Wistar Institute of Anatomy at Phila- 

 delphia. 



Piroplasma (L. pirum, pea -f G. plasma, a 

 formed thing). Piroplasmas are pear 

 shaped parasites of red blood cells caus- 

 ing diseases of great importance in 

 domestic and other animals but not as 

 yet found in man. They can be colored 

 by any good blood stain. Giemsa and 

 May-Giemsa are recommended. 



Pituitary. The microscopic techniques for 

 this conductor of the endocrine sym- 

 phony are obviously too numerous to 

 mention. Consult each issue of the 

 Quart. Cum. Index Med. 



To differentiate 2 classes of acido- 

 philes in the cat a modification of 

 Heidenhain's "azan" modification of 

 Mallory's connective tissue stain is 

 proposedby Dawson, A. B. and Friedgood, 

 H. B., Stain Tech., 1938, 13, 17-21. T. 

 Maxwell, Jr. (ibid, 93-96) proposes a 

 modification especially designed for the 

 basophiles and Koneff, H. H. {ibid, 49- 

 52) one for the rat. In addition all 

 within the space of a few months, Lewis, 

 M. R., and Miller, C. II., Stain Techn., 

 1938, 13, 111-114 give following direc- 



tions to demonstrate 2 types of granular 

 cells in the pars nervosa. Vix in 3% 

 aq. potassium bichromate 2 parts and 

 half sat. corrosive sublimate in 95% 

 ale. 1 part, 12-24 hrs. with 1 change. 

 Dehydrate to 70% alcohol to which add 

 few drops iodine. Change each day 

 until solution retains color. Dioxan, 

 8-24 hrs., 3 changes. Dioxan -|- little 

 paraffin. Paraffin 4 changes. Cut sec- 

 tions 4 microns and deparaffinize. Stain 

 0.25% aq. acid fuchsin 30 min. Then 

 1-24 hrs. in Mallory's stain (aq. dest., 

 100 cc; anilin blue, 0.5 ^m.; orange G, 

 2 gm. and phosphotungstic acid, 1 gm.). 

 Differentiate in 95% alcohol until no 

 more color comes out. Abs. ale, xylol, 

 balsam. To identify microglia in neuro- 

 hypophysis see Vazquez -Lopez, E., J. 

 Anat., 1942, 76, 178-186. Differential 

 stain for mouse pituitary (Dickie, M. 

 M., Science, 1944, 100, 297-298). Pitui- 

 cytes by Hortega silver carbonate tech- 

 nique (Shanklin, W. M., Stain Techn., 

 1943, 18,87-89). 

 Placenta — Written by Dr. George B. 

 Wislocki, Dept. of Anatomy, Harvard 

 Medical School, Boston 15. March 8, 

 1951 — Of all the organs of the body the 

 placenta has been the least investigated 

 by histological, cytological and cyto- 

 chemical methods. Compared to most 

 other tissues, its study is greatly com- 

 plicated by the marked and perplexing 

 differences in its structure in various 

 mammals, as well as by the fact that 

 from the moment of implantation up to 

 the time of parturition, it goes through 

 a complex succession of structural 

 changes. The latter are doubtlessly 

 related to differing physiological and 

 nutritional needs, first of the implant- 

 ing egg, then of the differentiating em- 

 bryo before the heart has begun to 

 beat, and finally of the growing and 

 maturing fetus. Besides subserving 

 the immediate needs of fetal nutrition 

 and of excretion of fetal waste products, 

 the placenta is also an endocrine organ 

 which produces both steroid hormones 

 and chorionic gonadotropin. Rela- 

 tively little is known concerning the 

 functions of these hormones, but the 

 placental steroids apparently play an 

 important part in the growth, regula- 

 tion and maintenance of the pregnant 

 uterus by exerting their influence prin- 

 cipally upon the uterine musculature 

 and blood vessels and thereby influenc- 

 ing also the length of gestation and the 

 onset of labor. The role of chorionic 

 gonadotropin is more obscure, but it 

 seems to interplay with the pituitary, 

 as well as with the steroid-producing 

 glands including the placenta itself. 



