CLASSIFICATION OF ANIMAL PEEPAKATIONS. 443 



understanding of the structure of mucous membranes and 

 glands been obtained. The methods to be adopted for the 

 examination of mucous membranes in general by the micro- 

 scope will here be given. 



Method of Examining the Surface of Mucous Membranes. — 

 Supposing, for example, the specimen to be examined be a 

 portion of the mucous membrane of the stomach of an animal 

 recently killed, the surface will be found to be covered over 

 by a thick layer of more or less viscid mucus ; this should be 

 got rid of by as gentle means as possible ; the best plan, on 

 the whole, perhaps, is that of allowing a small stream of water 

 to flow on it ; or, if the specimen be small, it may be pinned 

 out upon one of the loaded corks described at page 350, and 

 well washed by means of the small syringe also described at 

 page 351 ; if the epithelium be required for examination, a 

 small portion of it may be detached from the surface by a 

 scalpel, placed on a glass slide, and viewed as a transparent 

 object with a power of two hundred diameters. But if the 

 mucous membrane itself be required to be examined, it should 

 be done under water, the specimen being pinned out on a 

 loaded cork, and placed in a tin trough with a sufficient 

 quantity of that fluid to cover its entire surface ; if necessary, 

 the light of an argand lamp may be condensed upon it ; the 

 microscope to be employed for the examination may be one of 

 the kinds shown by figs. 32 and 37 ; and if the trough be too 

 large to be admitted upon the stage of an ordinary compound 

 instrument, that represented by fig. 237 wiU be found the 

 most convenient ; this method of examination will answer for 

 specimens either injected or not, and should be the one first 

 adopted. In order to obtain a correct idea of the external 

 surface, sections, both horizontal and vertical, should after- 

 wards be taken and submitted to high powers, and when the 

 membrane cannot be well cut into thin slices, it may be 

 separated by the needles, or by moderate pressure in the 

 compressorium. The plan of separation by needles will 

 succeed very well when the tubular portion of the stomach is 

 very thick, as in the case of the porpoise ; many tubes may 

 then be detached that could not have been so easily separated 



