154 PRACTICAL HISTOLOGY. 



is still alive, and in parts which are transparent 

 enough to allow the vessels to be distinctly seen. 

 Membranous parts are those which are naturally 

 best adapted for such observation, as, for example, 

 the web of the frog's foot and of the bat's wing ; 

 the tongue, mesentery, and lungs of the frog and 

 toad, but especially the latter animal ; and the 

 mesentery and omentum of small mammals. In such 

 preparations the surrounding tissues, and especially 

 the connective tissue corpuscles, may be studied as 

 well as the bloodvessels ; and the changes due to 

 commencing inflammation which are exhibited by 

 the bloodvessels, and the migration from the veins 

 of the white blood corpuscles, can always be brought 

 on either by the application of irritants, or, as in 

 the case of the serous membranes, hy simple expo- 

 sure to the air. The best methods, therefore, of 

 observing the circulation of the blood in different 

 parts will be described in the following preparations. 

 Preparation 6. Circulation in the frog's 

 web. One of the common English frogs (Rana 

 temporaria), of as light a color as possible, is chosen, 

 and by means of a Pravaz or other hypodermic 

 syringe two drops of a very weak solution of curare 

 (1 to 2000 of water) are injected under the skin of 

 the back. This is generally sufficient, in the course 

 of from a quarter to half an hour, to render the 

 animal completely motionless, whilst the pulsations 

 of the heart and the circulation proceed unimpaired. 

 The frog is then laid on a piece of cork or soft wood 

 of an oblong shape which* has a narrow slit at one 

 end. One of the interdigital webs is placed over 

 this slit and fastened on either side by means of one 

 or two minnikin pins or fine needle-points passed 

 through the adjoining webs. Care must be taken 

 that the web under examination is at no part tightly 

 stretched, since this would tend to arrest -or obstruct 

 the circulation. A slip of blotting-paper or a piece 

 of linen rag is placed over the animal and kept 

 thoroughly wetted with water, and the cork, with 



