CHANGES IN THE CIRCULATION. 305 



Through a third hole passed a horizontal glass tube. Now, when the 

 kidney increased in volume it drove the oil into the horizontal glass 

 tube, when it contracted the oil was sucked back again hence by 

 measuring the distance the oil advanced or retreated, the correspond- 

 ing increase or diminution of size of the kidney could be exactly de- 

 termined. 



The physiological importance of the changes of the volume of a 

 single organ was thus clearly established. If it was possible to record 

 those changes in an isolated organ, why not try to record them of a 

 part, a limb still connected with the body ? The possibility conceived 

 was soon accomplished. The apparatus was altered and improved. 

 In its new form it could be used to record the changes in the volume 

 of the human forearm by tracing them upon a piece of paper in the 

 shape of a series of curves. 



The construction of the apparatus, as finally adopted by Mosso, is 

 shown in the accompanying woodcut, copied from the original memoir * 

 of its inventor, who calls his instrument a plethy sinograph (pletismo- 

 grafo), because it writes the filling (plethitsmo) and unfilling of an 

 object. 



The apparatus consists of 



1. A glass cylinder, A B, forty-eight centimetres long and eight or 

 ten in diameter, open at one end, and terminating in a small neck at 

 the other. It is furnished with two openings, C and D, which serve to 

 fill it with water and to introduce a thermometer. These openings 

 may be closed with corks. The arm of the person to be experimented 

 upon is introduced into this cylinder. 



2. A broad ring at A of vulcanized rubber to fit around the end of 

 the cylinder and around the arm introduced into it, so as to form a 

 water-tight joint. 



3. A board, E, suspended from above, and serving to support the 

 glass vessel, with the included arm. 



4. The recording instruments. These have a difficult office to per- 

 form, for they must register the changes in the volume of the limb. 

 The forearm is placed in the cylinder A B, which is then filled with 

 water ; when the arm swells, the water is driven out through the rub- 

 ber tube F ; when the arm shrinks, the water is sucked back. Now, it 

 is the amount of water expelled or drawn in which is to be measured 

 this is accomplished by the following means : The rubber tube F opens 

 into a glass tube G, which, bending at right angles, descends to the 

 level a b of the licmid contained in the large beaker P. The descend- 

 ing limb is perfectly vertical, and securely fixed in that position by 

 being fastened to an iron support. A thin-walled test-tube, M, about 

 eighteen centimetres long, is suspended by two silk threads from the 

 double wheel L, and balanced by a counter weight N, which also car- 



* " Sopra un nuovo Metodo per scrivere i Movimenti dei Vasi Sanguini nell' Uomo." 

 " Atti della Reale Accademia delle Scienze di Torino," vol. xi (November 14, 1875). 

 VOL. xvii. 20 



