526 A MANUAL OF PHYSIOLOGY 



Note that dextrin (erythrodextrin) gives the same colour with 

 iodine as glycogen does. Dextrin is also precipitated by alcohol, 

 but a greater proportion must be added to cause complete precipita- 

 tion. Glycogen is completely precipitated by saturation with mag- 

 nesium sulphate or ammonium sulphate, while a pure solution of 

 erythrodextrin is not precipitated. Basic lead acetate also pre- 

 cipitates glycogen, but not dextrin. Maltose is formed when dextrin 

 is digested with saliva. 



(c) Cut another oyster into pieces, throw it into boiling water 

 acidulated with dilute acetic acid, and boil for a few minutes. Rub 

 up in a mortar with sand, boil again, and filter. Test a portion of 

 the filtrate with iodine for glycogen. Precipitate the rest with alcohol, 

 filter, dissolve the precipitate in water, and test again for glycogen. 



(2) Deeply etherize a dog or rabbit five hours after a meal rich in 

 carbo-hydrates (e.g., rice and potatoes). Fasten it on a holder. Clip 

 off the hair over the abdomen in the middle line. Make a mesial 

 incision through the skin and abdominal wall from the ensiform car- 

 tilage to the pubis. The liver will now be rapidly cut out [by the 

 demonstrator] and divided into two portions, one of which will be 

 [distributed among the class and] treated as in (a) or (^) ; the other 

 will be kept for an hour at a temperature of 40 C., and then sub- 

 jected to process (a) or (b). Little, if any, sugar and much glycogen 

 will be found in the portion which was boiled immediately after 

 excision. Abundance of sugar will be found in the portion kept at 

 40 C. ; it may or may not contain glycogen. 



2. Catheterism. In many physiological experiments it is neces- 

 sary to obtain urine from the bladder by means of a catheter. The 

 most suitable form for animals is the flexible vulcanized rubber tubes, 

 which are also often employed in man. It is possible to pass a fine 

 catheter into the bladder of a male dog. A larger one is easily 

 passed in a male rabbit, and a still larger in a bitch, which is often 

 used for experiments on metabolism. Even in the bitch the opening 

 of the urethra lies entirely concealed within the vagina, much 

 deeper than the cul-de-sac in the mucous membrane, into which 

 the beginner usually tries to force the catheter. For a first attempt 

 the animal should be etherized and fastened on a holder. The little 

 or index finger of the left hand is passed into the vagina till the 

 symphysis pubis can be felt. A little below this is the opening of 

 the urethra. With the right hand the point of a flexible catheter of 

 suitable calibre is directed along the finger, and after a little ' guess 

 and trial' it slips into the bladder, its entrance being announced 

 by the escape of urine. 



When the bitch is to be used in a long series of experiments an 

 operation is sometimes performed first of all to render the urethral 

 orifice more accessible. 



3. Glycosuria. (i) Weigh a dog (female by preference) or rabbit. 

 Give morphia to the dog or chloral to the rabbit, as described on 

 pp. 176, 190. Fasten on a holder, and etherize. Insert a glass cannula 

 into the femoral or saphena vein of the dog, or into the jugular of 

 the rabbit (p. 177). Fill a large syringe with a 2 per cent, solution 



