PLATELET COUNTS 



276 



PNEUMONOCYTES 



techniques are only required to reveal 

 the organization of the ground sub- 

 stance, holding the chlorophyll, and 

 their r61es in photosynthesis. A full 

 account is provided by Guilliermond, 

 A., The Cytoplasm of the Plant Cell. 

 Waltham: Chronica Botanica Co., 1941, 

 247 pp. (translated from the French by 

 L. R. Atkinson). 



Platelet Counts, see Blood Platelets. 



Plastosomes, see Mitochondria. 



Platino-Acetic-Osmic mixture, see Her- 

 mann's Fluid. 



Platinum. Intravenous injections of col- 

 loidal solutions of platinum in rabbits 

 are described by Duhamel, B. G., C. 

 rend. Soc. de Biol., 1919, 82, 724-726. 

 For microchemical detection of plat- 

 inum reference is made to the method 

 of Okamoto and Associates as described 

 by Click (p. 26). 



Platinum Chloride is the name usually given 

 to hydro-chloroplatinic acid. It is used 

 occasionally as an ingredient of fixa- 

 tives. 



Platyhelminthes is the phylum of flatworms. 

 The two classes of important parasites 

 are the Cestodes and Trematodes. 

 See Parasites. 



Pleuropneumonia. Staining of organisms. 

 Stain paraffin sections 4 microns thick 

 of tissue fixed in Zenker, Bouin, abso- 

 lute alcohol or Carnoy's fluid brought 

 down to water directly in Mallory's 

 phosphotungstic acid hematoxylin (18- 

 24 hrs.) without preliminary treatment 

 with permanganate and oxalic acid. 

 Do not wash but blot nearly dry and 

 dehydrate rapidly in absolute alcohol, 

 clear in xylol and mount in balsam. 

 Organisms in lungs appear as deep blue 

 masses of mycelial threads (Turner, H. 

 W., Austral. J. Exp. Biol. & Med. Sci., 

 1935,13,149-155). 



Plehn's Stain for malaria plasmodia is de- 

 scribed by Craig, p. 289 as uncertain in 

 its action and is not recommended if 

 other modifications of Romanowsky 

 stain are available. 



Plimmer's Bodies, see Bird's Eye Inclu- 

 sions. 



Plutonium. Use of micrurgy in study of 

 chemical properties of first micro- 

 quantities of plutonium, Seaborg, G. T., 

 Science, 1946, 104, 379 also Chambers, 

 R. W. and Kopac, M. J. in McClung's 

 Microscopical Technique, 1950, p. 543. 

 Pneumonocytes — Written by C. C. Macklin, 

 Dept. of Histological Research, The 

 University of Western Ontario, London, 

 Canada. November 28, 1951— These 

 elements are also known as pulmonary 

 cells (la cellule pulmonaire), epicytes, 

 septal cells, niche cells, alveolar epi- 

 cytes, alveolar cells, alveolar wall cells, 

 alveolar granular cells, alveolar epi- 



thelial cells, residual epithelial cells on 

 the pulmonary alveolar walls, little 

 granular cells, etc., and are demon- 

 strable in mammalian lungs by the 

 usual methods of fixation and staining. 

 Their most prominent feature is an 

 array of Vacuoloids (which see) in the 

 cytoplasm (Macklin, C. C, Anat. Rec. 

 1947, 97, 397). This gives to them in 

 ordinary sections a frothy appearance. 

 Many contain phagocytized particles. 

 The latter are the mural phagocytes or 

 dust cells (which see). They are found 

 inserted into canals in partitional al- 

 veolar walls, which, when vacated, are 

 natural pores. In the marginal alveolar 

 walls they are inserted into sockets. 

 Most are lodged in crotches of adjoin- 

 ing alveolar walls. Normally they are 

 5m to 15/x in maximum diameter, but 

 when stimulated exceed this size. 



The form is altered by the fixation 

 technique employed to demonstrate 

 them. After perfusion of the pul- 

 monary blood vessels of the unopened 

 thorax with physiological saline solu- 

 tion followed by a fixative such as 

 Bouin's fluid, the pneumonocytes of 

 partitional alveolar walls often in pro- 

 file have the shape of a carafe with 

 larger head and attenuated foot, and 

 a connecting stalk which is indented 

 by the environing capillary. In ma- 

 terial fixed by immersion of a block of 

 lung tissue the cell often appears 

 rounded with little or no indication 

 that it extends from one alveolus to 

 another. When fixation was by filling 

 of the air spaces with preservative the 

 cell is often extended laterally, that 

 is flattened, and appears wider and 

 shorter than normal. Probably the 

 best preservation of normal form is 

 attained in the mouse by immersion 

 of the unopened thorax, cleared of skin 

 and muscle, in fixing fluid. In such 

 preparations the cell, when situated in 

 an alveolar "corner" may show as 

 many as four separate air faces, and a 

 cytosome often forked in longitudinal 

 section (Macklin, C. C, Trans. Roy. 

 Soc. of Canada, Sect. V, 1946, 40, 93- 

 1 1 1 — bibliography) . 



H. von Hayek, Anat. Anz., 1942, 93, 

 149-155, estimated their combined 

 volume in both human lungs to be 150 

 cubic centimeters; and they would thus, 

 in his view, compose a diffuse intra- 

 pulmonic alveolar epithelial organ as 

 large as the spleen of man. Sjostrand 

 and Sjostrand (Zeitsch. f. mik.-anat. 

 Forsch., 1938, 44, 370-411) give their 

 combined volume as 10% of the lung 

 tissue. 



From them tumors may originate in 

 man and the lower mammals. Mostofi 



