POSTMITOTIC CELLS 



285 



POTASSIUM 



excreted in the urine. Protoporphyrin, 

 which is now known to be the same as 

 ooporphyrin, is excreted in relatively 

 large amounts by female birds. A 

 porphyrin-secreting gland deposits this 

 on the egg shell as it passes through the 

 oviduct. The purpose of this is not 

 known. Protoporphyrin and copropor- 

 phyrin develop in abundance in eggs as 

 they are incubated and embryonic tis- 

 sues and fluids in general have a rela- 

 tively high porphyrin content. Graf- 

 lin, A. L., Am. J. Anat., 1942, 71, 43-64 

 gives the technic for histochemical 

 studies of the protoporphyrin in rat 

 harderian glands. This includes sev- 

 eral good illustrations. These glands 

 excrete porphyrins which pass via the 

 naso -lachrymal duct and larynx to the 

 gastro-intestinal tract (Figge and Salo- 

 mon, J. Lab. & Clin. Med., 1942, 27, 

 1495-1501). Most of the porphyrin in 

 the feces of rats is derived from the 

 harderian gland excretions. In addi- 

 tion to rats, mice also excrete relatively 

 large amounts of protoporphyrin via 

 the harderian glands. The variability 

 with respect to the red fluorescence of 

 the harderian glands of mice of strains 

 with different susceptibility to spon- 

 taneous mammary carcinoma gave rise 

 to the hypothesis that porphyrins were 

 involved in the regulation of suscepti- 

 bility to mammary carcinoma (Figge, 

 Strong, Strong, Jr., and Shanbrom, 

 Cancer Res. 1942, 2, 335-342). Ham- 

 sters, which are very susceptible to 

 chemically-induced tumors, were also 

 found to have brilliant red fluorescent 

 harderian glands. The occurrence of 

 porphyrins in certain organs and tissues 

 of the human subject which exhibit a 

 high cancer incidence (cervix of uterus, 

 skin, etc.) led to the concept that these 

 substances may act as co-carcinogens in 

 a more general manner than postulated 

 at first (Figge, A. A. A. S., 1945, 117- 

 128). Jones, E. G., Shaw, H. N., and 

 Figge, F. H. J., Am. J. Obs. & Gyn., 

 1946, 51, 467-479 give technics for 

 demonstrating porphyrin on the cervix 

 of the uterus in the human subject. 

 See Hematoporphyrin. 



Postmitotic Cells, see Cell Classification. 



Postmortem Change. These are alterations 

 in structure due to autolytic and os- 

 motic changes. The rate of autolysis 

 is very rapid in some organs such as the 

 pancreas which are enzyme producers. 

 It is relatively slow in the walls of elas- 

 tic arteries in which the proportion of 

 inanimate components (elastic and col- 

 lagenic fibers) is high. In the case of 

 tissues which cannot be immediately 

 fixed certain precautions should be 

 taken to minimize postmortem change. 



See Agonal Changes, Artifacts, Fixa- 

 tion, and Small Intestine, Necrosis, 

 Necrobiosis. 



Potocytosis, a term introduced by Meltzer 

 to designate submicroscopic "sipping" 

 of fluid by cells. See Pinocytosis. 



Pottenger's Dilution Flotation method, see 

 Concentration of bacteria. 



Potassium, Histochemical methods. 



1. Policard, A. and Fillet, D., BuU- 

 d'Hist. Appl., 1926, 3, 230-235 have sug- 

 gested that potassium and sodium prob- 

 ably occur as chlorides and that their 

 conversion to sulphates by treating the 

 sections with sulphuric anhydride fumes 

 makes them more stable and better able 

 to withstand the high temperature of 

 Microincineration which see. 



2. Marza, V. D., Bull. d'Hist. Appl., 

 1935, 13, 62-71 has modified Macallum's 

 well known technique. Fix small pieces 

 of tissue in 96% pure ale. in the ice box. 

 Make paraffin sections. To eliminate 

 the possibility of the presence of iron 

 leave {control sections 5 min.in freshly 

 prepared sol . yellow ammonium sulphate . 

 Wash in aq. dest., dehydrate, clear and 

 mount in neutral balsam. There should 

 be no ppt. Make up following solu- 

 tions: A. Cobalt nitrate, 5 gm.; aq. 

 dest., 10 cc; glacial acetic acid, 2.5 cc. 

 B. Sodium nitrite, 25 gm.; aq. dest., 36 

 gm. To A add 41 cc. of B and use 

 immediately. If delay is necessary 

 keep in ice box and filter before using. 

 Cover test sections with this for 2 

 hrs. in a closed Petri dish to avoid 

 evaporation. Wash slowly in 50% ale. 

 to remove every trace of reagent. 

 Plunge in ammonium sulphate solution 

 3 min. Wash in aq. dest. to remove 

 ammonium sulphate. Dehydrate, clear 

 and mount. Examine illustrated paper 

 by Marza and Chiosa (V. D. and L. T., 

 Bull. d'Hist. Appl., 1935, 13, 153-177) 

 on application of this method to the 

 problem of ovogenesis. 



3. Gersh, I., Anat. Rec, 1938, 70, 

 311-329 has also modified Macallum's 

 method. It involves the making of 

 similar paraffin sections as for Chloride, 

 which see. Transfer these to a fairly 

 large cool room (—1° to -f 1°C.) and re- 

 move paraffin and petroleum ether as 

 for chloride. Cover with 12% sodium 

 cobalti-nitrite solution of Biilman 

 (Treadwell, F. P., Analytical Chemis- 

 try, vol. 1, 4th English Ed. translated 

 by W. T. Hall, New York, John Wiley 

 & Sons, Inc., 1916, p. 81). Decant 

 fluid, mount in glycerin in same way and 

 examine. Crystals of sodium potassium 

 cobalti-nitrite are just visible with oil 

 immersion lens. They are short yellow 

 rods with rounded ends in a diffuse pale 



