PRACTICAL EXERCISES 427 



colour, and thus obscures the rose reaction. If still 

 more cupric sulphate be added, blue cupric hydroxide 

 is thrown down, and nothing can be inferred as to 

 the presence or the nature of proteins in the liquid. 

 (y) Heat another portion of the nitrate from (a) to 30 C., 

 and add crystals of ammonium sulphate to satura- 

 tion. A precipitate of proteoses (albumoses) may 

 be obtained. Filter off. 



(5) Add to the filtrate from (y) a trace of cupric sulphate 

 and excess of sodium hydroxide. A rose colour in- 

 dicates that peptones are present. More sodium 

 hydroxide must be added than is sufficient to break 

 up all the ammonium sulphate, for the biuret 

 reaction requires the presence of free fixed alkali. 

 A strong solution of the sodium hydroxide should 

 therefore be used, or the stick caustic soda. The 

 addition of ammonium sulphate will cause the red 

 colour to disappear ; so will the addition of an acid. 

 Sodium hydroxide will bring it back. Ammonia 

 does not affect the colour. 



(e) Use another portion of the filtrate from (a) to separate 

 the primary and secondary albumoses as in experi- 

 ment (2) (y) (p. 10). 



(e) To some milk in a test-tube add a drop or two of rennet 

 extract, and place in a bath at 40 C. In a short time the milk is 

 curdled by the rennin. (See p. 326.) 



5. (i) To obtain Normal Chyme. Inject subcutaneously into a 

 dog, one and a half hours after a meal of minced meat and water, 

 2 mg. of apomorphine. Half of one of the ordinary tabloids is 

 enough. Collect the vomit. 



(2) To obtain Pure Gastric Juice. If the laboratory possesses a dog 

 with Pawlow's double resophageal and gastric fistula, the juice may 

 be obtained in large amount by sham feeding with meat (p. 374). If 

 not, proceed as follows : Put a fasting dog 

 under ether, and fasten on the holder. Clip 

 the hair and shave the skin in the middle 

 line below the sternum. Make a longi- 

 tudinal incision through the skin and sub- 

 cutaneous tissue from the xiphoid cartilage 

 downwards for 3 or 4 inches. The linea 

 alba will now be seen as a white mesial 

 streak. Open the abdomen by an incision 



through it. Pull over the stomach towards FlG - 158. STOMACH 

 the right, and stitch it to the abdominal CANNULA. 



wall, open it, and insert a stomach cannula 



(Fig. 158). Make an incision through the serosa and muscularis. 

 Doubly ligate and divide any vessels exposed in the submucosa. 

 Then make an opening in the mucosa of sufficient size to just 

 admit the gastric cannula. This will go into a smaller opening 

 if it is provided with a nick in the flange which enters the 

 stomach. Be careful to prevent blood from getting into the 

 stomach. Immediately stitch the wound in the stomach over the 

 flange of the cannula, but do not pass the stitches through to the 

 internal surface of the mucosa. Suture the muscles and skin 

 separately. Then stitch up the wound in the abdomen. Wash 

 out any stomach contents with warm water. Put a cork in the 



