Page:The New International Encyclopædia 1st ed. v. 13.djvu/510

* MICROSCOPY. 458 MICROSCOPY. speoiiucu oil the cuvir glass, the cover glass is passfd through a blue flame of sudicient lieat to liriug the specimen just to the boiliiij; point of water. The specimen may now be stained by placing upon it a few drops of a -natery solution of fuehsin, gentian violet, or methylene blue. After staining it is washed in water and may then be examined. For other organisms more rarely present in urine the reader is referred to special works upon microscopical urinalysis. Blood. The main piirposes for which blood is examined microscopically are as follows; ( 1 ) To determine the number of red blood cells. (2) To determine the richness of the red cells in htemoglobin. (31 To determine the size, shape, etc., of the red cells and the presence of forms of cells not foind in normal blood, e.g. nucleated red blood cells. (4) To determine the number of white blood cells. (5) To determine the relative proportion of the different kinds of white blood cells — 'differen- tial count of leucocytes.' (ij| For the Plasmodium malariie. ( 7 ) In suspected typhoid for Widal's reaction. (8) For bacteria and other foreign substances. For description of the normal histology of blood the reader is referred to the article on Blood. Counting the Red Blood Cells. This is best accomplished by means of Thoraa's hoematocyto- nieter or blood-counting apparatus. This consists of a pipette with bulb and graduated capillary tube. The graduation of the tube is 0.5 and 1, that of the bulb and tube together 100. By filling the tube to mark 1 with blood and then the bulb and tube to mark 100 with an inert diluting fluid such as normal saline, a dilution of 1 to 100 is obtained. The counting slide has in its centre a round chamber, in the centre of which is a raised flat glass surface which is marked off into 400 equal squares, each of which is one four-hundredth of a square millimeter. The surface of the marked-off area is just one-tenth of a millimeter lower than the surface of the rest of tlic slide. A drop of the diluted blood is placeil upon the centre of the graduated area and a flat cover glass placed over it. As will be seen, the auiount of fluid over one of the small squares is one-tenth times one four-hun- dredth or one four-thousandth of a cubic milli- meter. The number of cells in one square is then counted. This nuiltiplied by 4000 and then by the dilution, 100, gives the result desired, i.e. the number of red cells in one cubic millimeter of blood examined. In actual practice a large number of squares is coinlcd and the average taken. The white blood cells may l)e counted in the same specimen if desired. Owing, however, to their smaller number, a larger number of squares should be counted to avoid error. For determin- ing the richness of the individual corpuscles in ha-nioglobin, the shape and size of the cells, the relative number of the different kinds of white cells, the presence of the malaria plasmodium, etc., the preparation of fixed and stained speci- mens is reipiired as follows. Blood from a needle prick is taken up on the end of a glass slide and thi.** is drawn across the surface of a seconcl slide. thus making a thin 'smear' of blood. This is dried quickly in the air, after which it is 'fixed' by equal parts of alcohol and ether, the vapor of osmic acid or of formalin, or by subjecting to the action of dry heat. The specimen is now ready for staining. A combination of eosiu and methylene blue, and Ehrlieh's triacid stain, are the most satisfactory. After staining the speci- men is washed in water. The eosin-methylene blue method is the most satisfactory for general purposes and stains the malaria plasmodium. Ehrlieh's stain is most satisfactory for making a differential count of the leucocytes. Persistent marked reduction in the number of red cells occurs in primary jjernicious am^mia and in the severe secondary ana'uiias due to some of the infectious diseases. It may also be due to the action of certain mineral poisons (phos- phorus, arsenic, etc.), to long-continued suppura- tive processes, cancer, malaria, conditions of malnutrition, etc. Loss in the hiemoglobin content of the indi- vidual cells occurs especially in that form of ancemia known as chlorosis, iloderate diminu- tion in numljer of cells may also occur. In leu- cocythicmia there may also be both a reduction in the number of cells and a reduction in hiemo- globin content. This loss on the part of the indi- vidual cell in hiemoglobin is shown in the eosin- stained specimen bv an increase in the clear cen- tral area of the cell. Irregular red cells (poikilocytes), small red cells (microeytes), and large red cells (megalo- cytes) are found in severe antemias whether pri- mary or secondary. Xucleated red blood cells are found in all forms HUMAN BED BLOOD CORPUSCLES AND TWO LEUCOCYTES. of ana-mia. As they represent developmental types, their presence may be construed as an attempt on the part of nature to replace lost cells. Very large nucleated red cells (megalo- lilasts and gigantoblasts) are sometimes present in severe anaemias. Moderate increase in the number of white blood cells occurs physiologically during the first few days after birth, in the later months of preg- nancy, and after eating. Pathological increase in the numl)er of white cells occurs in many of the infectious diseases, especi.illy those accompanieil by exudation or suppuration. It is notably ab- sent in typhoid, t.vphus, tuberculosis, measles, and malaria. Lymphocytosis, or increase in the num-