10 PRACTICAL PABASITOLOGY 



details of preparation, should be carried out either in a test-tube, by the 

 method described in the chapter upon Examination of the Blood, or 

 under the cover-glass, the superfluous liquid being drawn off by means 

 of filter paper from one edge, while fresh liquid is allowed to flow in 

 at the other. 



The cover-glass preparations when fixed are subjected to the same 

 finishing processes (rinsing, hardening in alcohol, staining, transference 

 to xylol and Canada balsam) as other specimens. The simplest and 

 best method of storing them is in 70 to 80 per cent, alcohol in 

 well-corked glass tubes, the inner diameter of which is slightly larger 

 than that of the cover-glasses. The specimens are placed back to 

 back in pairs and are kept from moving by means of a cotton- wool 

 pad. If long tubes are used, several pairs may be arranged above 

 one another. They should be separated by cotton-wool pads, and, 

 for the sake of convenience, should be placed at right angles to one 

 another. 



The preparation of sections is essential, not only to a right under- 

 standing of the relationship of the parasite to the tissues of its host, 

 but also to a proper appreciation of details of structure and develop- 

 ment, many of which are not seen in the intact Protozoon, or only 

 to a very imperfect extent. For the method of their preparation 

 reference must be made to the various text-books of medical 

 microscopy. There is one item of the technique, however, for which 

 I propose to give detailed instructions, that, namely, of embedding, for 

 the purpose of cutting single minute Protozoa into sections. 



As a general rule, the Protozoa will be present in some numbers, 

 and in that case it will rarely be necessary to arrange them in a given 

 fashion before embedding. After fixing, the animalcules should be 

 transferred to a small glass tube, where the various stages of the process 

 should be carried out, including the spirit grades and the treatment 

 with cedar wood oil (xylol or some other intermediary) to the final 

 embedding in paraffin. It is better to centrifugalize each time before 

 changing the liquid. Unless this is done, as, for instance, in the 

 absence of a proper centrifuge, it will be necessary to wait until the 

 micro-organisms have fallen to the bottom of the tube, and then 

 carefully pour off the liquid, a glass rod being used to decant. As soon 

 as the objects are soaked through with paraffin, the paraffin is rapidly 

 cooled by plunging the glass tube into cold water. The tube may 

 now be shattered, leaving a solid block densely packed with Protozoa 

 which is ready for cutting. 



Where a centrifuge is not available it is more convenient to follow 

 an older method, recommended by Schaudinn. An arrangement similar 

 to the micro-aquarium for the cultivation of Amoebae, described on p. 15, 

 is used, but with this difference. The cut in the glass slide should 



