218 THE AMERICAN MONTHLY [October, 



For the application of gases a gas-chamber must be employed. Such 

 a piece of apparatus is shown in Fig. i . This is known as Strieker's 

 hot-stage and gas-chamber. It consists of a rectangular piece of ebon- 

 ite, e e, fixed to a brass plate that rests on the stage of the microscope. 

 On the upper surface of the ebonite is a brass plate, P, with an open- 

 ing in its centre, c, leading into a brass tube closed below with a piece 

 of glass. A cover-glass, upon which a thin layer of _ blood has been 

 spread, is inverted over the opening, c. The tube, «, is connected with 

 the gas generator by a rubber tube, upon which a spring clip is placed 

 for regulating the flow of the gas. The gas enters the chamber, c, 

 through this tube and escapes through the tube, a. 



In using this apparatus as a warm-stage, the copper wire, B, is placed 

 on the tube, a . Heat is applied to the wire by means of a Bunsen's 

 burner or alcohol lamp. The temperature of plate P, upon which the 

 slide is placed, is regulated by the distance of the flame from the stage. 

 The thermometer, /, indicates the temperature. 



The white cells can be studied in the fresh condition in the same 

 manner as described above for the red cells. In studying the amoeboid 

 movements of the white cells of the mammalia it is necessary that the 

 temperature of the prepai'ation should be kept at the body temperature 

 of the animal [37 C.], while in the cold-blooded animals the movements 

 take place at the ordinary room temperature. In order to keep the 

 preparation of the mammalian blood at the proper temperature, the 

 warm-stage, Fig. 1, is used. The preparation is made in the same 

 manner as for studying fresh blood. As the movements of the cells is 

 very slow it is difficult to perceive the changes in form, but if an active 

 cell is selected and sketches made of it at intervals of two minutes, one 

 will soon see that its form as well as its position has changed. 



Blood Placques. — Various solutions are recommended for studying 

 the blood placques in the fresh state. Bizzozero uses a \Ya solution of 

 sodium chloride, to which one part of methyl-violet is added for every 

 5,000 parts of salt solution ; Hayem uses his modification of Pacini : s 

 fluid; Zimmermann, a solution of sodium sulphate; Afanassiew, nor- 

 mal salt solution to which 0.5% of dried pepsin and 1 to 1,000 of methyl- 

 violet are added, with a few drops of carbolic acid to prevent decompo- 

 sition ; Osier, Pacini's fluid or a 1% solution of osmic acid. In all cases 

 the blood must pass directly into the preserving fluid. 



The method of examination is as follows : A drop of the fluid is 

 placed upon the finger tip, and the latter pricked with a clean needle, 

 so that a drop of blood passes into the fluid, which is then placed on a 

 slide and covered. The drop of blood must be small, and must be 

 quickly disseminated through the fluid with the point of the needle. 

 The preparation is to be examined with a power of about 500. 



For studying the placques in the circulation, the mesentery or omen- 

 tum of a small animal — young rabbit, white rat, or guinea pig — may 

 be used. On account of the rapidity of the circulation in the larger 

 vessels, it is difficult to make out the placques ; but if a small trans- 

 parent vessel, in which the current is moderately slow, be selected, 

 then the placques will be seen in the still layer mingled with the white 

 cells. If the current becomes very slow, the placques have a tendency 

 to collect along the periphery with the white cells. 



The placques may also be studied in the vessels of a recently-killed 



