2398 journal of Applied Microscopy 



recorded in his remarkable work on the distomes of fishes and frogs upon living 

 specimens in this way (Looss, Die Dist. Fisch. u. Frosch. Bibl. Zool. xvi. p. 3, 

 1894). 



It is not, however, necessary to have an expensive life-box or compressor to 

 employ this method successfully. In many instances a cover-glass of the ordinary 

 sort can be directly applied over the animal located beneath its center, and the 

 capillary attraction between the slide and cover relied on for the compression. 

 The degree of compression can be regulated by withdrawing water from beneath 

 the cover-glass with a piece of bibulous paper at the edge, and removing it at 

 the proper moment, or by adding water at the edge from a pipette. This simple 

 device serves very well for brief examinations, but on account of the constant 

 evaporation at the edge of the cover, it is not satisfactory where a specimen is 

 to be kept under observation during several hours, in which case the life-box 

 should be employed. 



Living specimens of Hydra compressed in either of these ways demonstrate 

 many points in the anatomy and histology very clearly indeed. Thus, the ordi- 

 nary ectoderm cells and the nematocysts, the endoderm cells in different parts of 

 the body and their differences in each locality are visible. 



In many of the smaller trematodes in the living state this method is very suc- 

 cessful indeed. It is, in fact, the best general method for studying these forms. 

 I have in mind at present its employment in the study of Cotylaspis, a small 

 fluke related to Aspidogaster and a frequent parasite of the fresh-water mussel, 

 in which it lives on the cloacal surface of the kidney. It is a small animal, 

 measuring about 2 mm. in length. By studying living specimens under com- 

 pression, all the organs and their connections can be by degrees demonstrated. 

 The details of histology are some of them shown in this way, too, and this is of 

 advantage for the sake of the corroboration it furnishes to the informa- 

 tion derived in the study of sections which have been subjected to the 

 operation of a great number of different reagents. The intestinal epithelium, 

 for example, is clearly seen and flame cells and the linings of the excre- 

 tory capillary and their cilia are recognizable. The larger flukes, even such 

 a large one as Distomum (Fasciola) hepaticum, while too large to permit as good 

 results as the smaller forms, will, when studied by this method, show a consider- 

 able part of the organization and greatly help one in the interpretation of sections 

 used to supplement the method. 



The process of compression can be applied to objects already preserved, 

 though not so effectively as to fresh ones. Thus, some time since, I wished to 

 put up a set of whole specimens of the common liver fluke for use in a zoology 

 class, from material which had been furnished me in alcohol. The worms had 

 died in any position they happened to assume. To correct this, I first soaked 

 them for a day in warm (30° C.) weak (30 per cent.) alcohol, till they were 

 flaccid and soft, then shaped them and placed them between two glass slides 

 and compressed them into a flat thin condition, as much so as could be done 

 without injury to the structure. Specimens thus compressed became quite thin, 

 and after subsequent handling gave excellent results. The later treatment was 

 as follows : First they were placed in strong alcohol while still under compres- 



