Beside this improved sphygmograph, Chauveau and Marey also invented the cardiograph, for the observation of the blood-pressure within the cavities of the heart. Their cardiograph was a set of very delicate elastic tambours, resting on the heart, or passed through fine tubes into the cavities of the heart,[1] and communicating impulses to levers with writing-points. These writing-points, touching a revolving cylinder, recorded the variations of the endocardial pressure, and the duration of the auricular and ventricular contractions. [1] "On peut s'assurer de l'innocuité de ce premier temps de l'expérience en examinant l'animal, qui n'est nullement troublé, qui marche et mange comme de coutume. En comptant le chiffre du pouls, on trouve quelquefois une légère accéleration, surtout dans les premiers instants; mais les mouvements du coeur sont toujours réguliers, et donnent, à l'auscultation, des bruits d'un caractère normal." (Marey, _loc. cit._ p. 63.) * * * * * It is impossible here to describe the subsequent study of those more abstruse problems that the older physiologists had not so much as thought of: the minutest variations of the blood-pressure, the multiple influences of the nervous system on the heart and blood-vessels, the relations between blood-pressure and secretion, the automatism of the heart-beat, the influence of gravitation, and other finer and more complex issues of physiology. But, even if one stops at Marey's book, now more than forty years old, there is an abundant record of good work, from the discovery of the circulation to the invention of the sphygmograph. II THE LACTEALS