LABORATORY WORK 197 



there are still some remaining, forming an inner granular zone 

 around the lumen. 



The observations are made by pithing the animal, opening 

 the body cavity, dividing the stomach along the greater curvature 

 and pinning one half of it over an opening in a plate of cork or 

 thin wood, with the muscular coat uppermost. It may be con- 

 venient to pin the newt on its side. The muscular coat is 

 sufficiently transparent to allow the deeper ends of the glands 

 to be examined under a fairly high power. If care be taken to 

 avoid loss of blood, it is possible to see the circulation around 

 the glands. The muscular coat may be snipped off by a fine 

 pair of scissors at some spot, if difficulty be found in seeing the 

 glands. 



Flow of Water. One of the forms of osmometer described on 

 p. 171 above is filled with a strong solution of congo-red, a fine 

 glass tube bent over at the top is inserted and the osmometer 

 immersed in distilled water. After a time, drops of dye solution 

 will issue from the upper end of the tube and may be collected. 



Electrical Change. Although this may be regarded as a some- 

 what difficult experiment for the student, it has much importance 

 in the general theory, and, at all events, it should be shown as 

 a demonstration. 



A sensitive high resistance galvanometer is required, such as 

 the Broca pattern made by the Cambridge Instrument Co. It 

 should be made as sensitive as possible by very careful adjustment 

 of the controlling magnet, so as to produce a long period of 

 oscillation. A spot of light from a lamp is reflected by the 

 mirror attached to the moving magnet and received on a divided 

 scale. If an arc lamp is used, the spot will be bright enough 

 to be visible at some distance. 



The tissue to be investigated must be led off by non-polarisable 

 (and equipotential) electrodes. The most convenient pattern is 

 that in which mercury and calomel are used. Take a small wide- 

 mouthed bottle, fitted with a paraffined cork through which three 

 glass tubes pass, two of these ending a short distance below the 

 cork, the other is longer. One of the two short ones is bent at 

 a right angle outside the bottle. The other short one is fitted 

 with a piece of rubber tube closed by a clip and is used for 

 filling. The third tube has a short piece of platinum wire fused 

 into the lower end, which is then sealed and contact made with 

 the platinum by pouring in a little mercury and dipping into 

 it a fine copper wire. This tube passes down into a layer of 

 mercury of a few millimetres depth at the bottom of the bottle 

 and makes contact with it by the platinum wire. Some calomel, 

 together with a little mercury, is rubbed in a mortar to a paste 



