34 THE DIGESTIVE ORGANS. 



The nerves in the taste-buds are brought out either by Golgi's 

 method, the methylene-blue method, or by the use of gold chlorid. If 

 the last be used the procedure is as follows : A papilla foliata of a rabbit 

 is removed with a sharp razor and placed for ten minutes in lemon juice* 

 then in gold chlorid for from three-quarters of an hour to one hour, after 

 which the specimen is placed in water weakly acidulated with acetic acid 

 (5 drops to 100 c.c. of water) and exposed to the light. As soon as 

 reduction has taken place the specimen is treated with alcohol and cut in 

 vertical sections. These may be treated for a short time with formic 

 acid (in which they swell slightly), washed with water, and mounted in 

 glycerin. 



In certain objects, such as the nictitating membrane of the frog, 

 certain lobules of the rabbit's pancreas (the latter being so thin as to be 

 especially well adapted for microscopic examination), etc., the glandular 

 structure may be examined in normal salt solution. 



Glands of the Digestive Tract. Microscopically, the glands pre- 

 sent varying pictures according to the phase of secretion in which they 

 are fixed. Specimens in the different stages may be obtained either by 

 feeding and then killing the animal after a definite period, or by irritating 

 certain nerves, or finally by the use of certain poisons especially adapted 

 to this purpose, such as atropin and pilocarpin. In the rabbit, for in- 

 stance, i c.c. of a 5% solution of pilocarpin hydrochlorate or i c.c. of 

 a 0.5% solution of atropin sulphate is used for each kilogram of the ani- 

 mal's weight. In atropin-intoxication secretion is suppressed, while in 

 pilocarpin-poisoning it is increased. By this method cells are obtained 

 either full of secretion or containing no secretion at all. 



Sections should be made from carefully selected material 

 which has been fixed either in Flemming's solution or corrosive subli- 

 mate, although fixation with strong alcohol also gives instructive pictures. 



In preparations fixed with Flemming's solution the crescents of 

 Gianuzzi stain somewhat more deeply than the remaining cells of the 

 alveoli, and in objects that have been treated with alcohol or corrosive 

 sublimate and then stained with hematoxylin the crescents take on a very 

 deep color. The intermediate tubules of the salivary glands also assume 

 a deeper stain with hematoxylin and carmin. The intralobular tubes are 

 particularly well defined by certain stains, as" for instance when Congo red 

 is used after staining with hematoxylin ; other acid anilin stains may 

 also be used. The intralobular tubes of most salivary glands (not, how- 

 ever, of the parotid of the rabbit nor of the sublingual of the dog) are 

 stained a dark -brown color (calcareous reaction) by agitating small, 

 fresh pieces of tissue in order to facilitate the entrance of air, and 

 then treating them with a dilute aqueous solution of pyrogallic acid. 

 The stain persists for some time in specimens preserved in alcohol. Sec- 

 tions made by free hand from tissues treated by this method .give excel- 

 lent results. 



Mucin is soluble in dilute alkalies, as for instance lime-water, 

 and may be precipitated from these solutions by the addition of acetic 

 acid, although the precipitate does not redissolve in an excess of acetic 

 acid ; mucin is also precipitated by alcohol, but not by heat. Mucin - 

 ogen does not stain with hematoxylin, as does mucin. By this latter test 

 a gland in a state of functional activity may be differentiated from one 

 at rest (R. Heidenhain, 83). After treatment with alcohol, safranin 



