vi CIRCULATION OF BLOOD: ITS DISCOVERY 179 



soon as the lung has readied the desired state of extension. To obviate the 

 inconvenience due t<> tin- convex surface of the organ, Holmgren invented a 

 little apparatus which consists of a special frog-holder, on which the animal 

 can lie. It has an opening clo.-ed liy a glass plate, above which a second 

 glass plate is fixed in a metal frame, which can be raised or lowered by a 

 screw. The lung, suitably inflated, is brought between these two plates, its 

 convex surface being flattened and adapted for observation by gentle pressure 

 of the upper plate. 



Anot hei- admirable subject for the observation of the circulation, which 

 was used more particularly by Cohnheim in his classical work on inflamma- 

 tion, is the frog's mesentery (r. Fig. 49, p. 176). The experiment is carried out 

 as follows : The ciirarised frog is laid on a cork plate, with a hole in its centre 

 to correspond with the aperture in the stage of the microscope, to which the 

 cork plate is fixed by clamps. Above the hole in the cork plate a ring, also 

 cut out of cork, is fixed by pins, the. upper edge of which has a depression 

 that serves to hold the bit of intestine fixed so as to stretch the mesentery. 



A lateral incision now has to be made in the frog's abdomen, avoiding the 

 lateral vein, when a loop of intestine is carefully drawn out with forceps, and 

 laid in the depression of the cork ring, so that the stretched mesentery lies 

 taut over the aperture of the ring. This la-ings the part under examination 

 to a higher level than the abdominal wound, otherwise it would become 

 charged with blood and serum escaping from the wound. 



The above ring is not required for observing the circulation in the 

 interdigital membrane or tongue of the frog, or in the tadpole's tail, etc., as 

 these can be simply fixed to the cork plate, by pins. When the observation 

 is to be prolonged for any length of time, it is necessary to prevent the parts 

 from drying up, which is done by placing over them little strips of filter- 

 paper soaked in physiological salt solution. The same method, with greater 

 precautions in regard to moisture and temperature, will serve for examining 

 the capillary circulation in warm-blooded animals, using, e.g., the mesentery 

 of mouse, guinea-pig, etc. 



BIBLIOGRAPHY 



For the history of discovery of the Circulation of the Blood, the reader is 



referred to the two following monographs, which comprise an enormous amount 



of research in original texts, and a clear and impartial criticism of ancient and 



modern contributions to the literature of this vexed question : 



G. CEUADINI. Ricerche storico-critiche intorno alia scoperta della circulazione 



del sangue. Milan, Fratilli Richiedei, 1876 (333 pp.)- Difesa della mia 



Memoria intorno alia scoperta della circulazione del sangue, contro 1' assalto 



dei signori H. Tollin teologo in Magdeburg, e W. Preyer fisiologo in lena. 



Con qualche nuovo appunto circa la storia della scoperta medesima. Genoa, 



1876. 



SIR MICHAEL FOSTER. History of Physiology. Cambridge, 1901. 

 R. WILLIS. Preface to Syclenham Edition of Harvey's Works. London, 1878. 

 M. ROTH. Andreas Vesalius Bruxelliensis. Berlin, 1902. 



For discovery of Lymph Circulation the fine article in Lipsius may be 

 consulted : 



W. His. Uber die Eutdeckung des Lymphsystems. Zeitschr. f. Anat. u. 

 Entwickelungsgeschichte, 1875. 



For discovery of Corpuscular Diapedesis, a complete account will be found in 

 the following memoir : 



P. HEGER. Etude critique et exp. sur 1'einigration des globules de sang, 

 envisages dans ses rapports avec I'inflanrmation. Brussels, H. Mauceaux, 



1878 (116 pp.). 



For Phagocytosis and Clieniotropism of Leucocytes see : 



E. METSCHNIKOW. Lei.-ons sur la pathologic comparee de 1'inflammation. Paris, 

 1892. 



