jyo SCIENCE PROGRESS. 



contraction. The effect on the blood-flow, and, therefore, 

 on the nutrition of the part supplied by such an arteriole, is 

 obvious. This partial contraction is called vascular tonus. 



Ludwig and his pupils mapped out accurately the 

 position of the vaso-motor centre. To Claude Bernard 

 belongs the merit of the discovery of the nerves which 

 influence the calibre of blood-vessels. On dividing the 

 sympathetic nerve in the neck of a rabbit he found that the 

 blood-vessels of the ear and face on that side flushed or 

 rather blushed, while stimulation of the distal end of the 

 nerve caused pallor of the corresponding parts. 



Perhaps one of the most important methods introduced 

 by Ludwig, but which grew gradually from small yet impor- 

 tant beginnings, is that of the nutrition of excised organs. 

 This method consists in circulating or perfusing blood or 

 other fluid through the blood-vessels of an excised or surviving 

 organ, i.e., when the excised organ possesses blood-vessels. 

 The fluid perfused may be blood or other fluid. The method 

 had its origin in the experiments conducted by Cyon and 

 also by Coats on the " isolated," i.e., "excised," frog's heart, 

 and gradually it grew in importance until it came to be one 

 of the most important methods used in studying the localised 

 action of drugs. 



This method depends on the fact that all our tissues or 

 organs do not die simultaneously. After so-called death 

 of the individual, the separate organs, especially in cold- 

 blooded animals, may retain their vitality for many hours 

 or even days. The heart of a frog or tortoise when cut out 

 of the body will beat under appropriate conditions for one 

 or two days. By means of this method the chemical and 

 other conditions necessary for cardiac activity were studied. 

 In studying the action of " surviving excised organs," e.g., 

 the frog's heart placed in connection with a recording 

 manometer, H. P. Bowditch, Professor of Physiology in 

 Harvard University, Boston (U.S.), showed that the muscle 

 of a frog's heart, quite independently of the strength of the 

 stimulus applied to it, either gave a maximal contraction or 

 it did not contract at all. On this A. Mosso, with that 

 Southern poetic spirit which characterises his way of look- 



