x ii PKEFACE. 



will bear with me if I try to make it more complete by here referring to 

 other scientific or historical works in which I have been engaged. 



In early life I had felt a strong desire to devote myself to the experi- 

 mental study of nature ; and, happening to see a glass containing some 

 camphor, portions of which had been caused to condense in very beauti- 

 ful crystals on the illuminated side, I was induced to read everything I 

 could obtain respecting the chemical and mechanical influences of light, 

 adhesion, and capillary attraction. Experiments I soon made in con- 

 nection with these topics are described in these memoirs. Some of 

 them I used in a Thesis for the degree of Doctor of Medicine in the 

 University of Pennsylvania. My thoughts were thus directed to physi- 

 ological studies, and I published papers on these topics in the Ameri- 

 can Journal of Medical Sciences. The favorable impression they made 

 caused me to be appointed, in 1836, Professor of Chemistry and Physi- 

 ology in Hampden Sidney College, Virginia, an appointment which en- 

 abled me to. convert experimental investigation, thus far only an amuse- 

 ment, into the appropriate occupation of my life. 



Several of the memoirs contained in this volume were composed at 

 that time. To them I was indebted, without any application on my part, 

 for an appointment to the Professorship of Chemistry and Physiology 

 in the University of New York. Soon afterwards I published a work 

 on the Forces that Produce the Organization of Plants. The lectures on 

 Physiology I gave at that time I improved from year to year, and at 

 length published them as a treatise on Human Physiology. It was very 

 favorably received by the medical profession. 



Among new experiments and explorations on physiological subjects 

 contained in that book may be mentioned the selecting action of mem- 

 branes ; cause of the coagulation of blood ; theory of the circulation of 

 the blood ; explanation of the flow of sap ; endosmosis through thin films ; 

 measure of the force of endosmosis; respiration of fishes; action of the 

 organic muscle fibres of the lungs ; allotropism of living systems ; new 

 observations on the action of the skin ; functions of nerve vesicles and 

 their electrical analogies ; function of the sympathetic nerve ; explanation 

 of certain parts of the auditory apparatus, particularly of the cochlea 

 and semicircular canals ; the theory of vision ; the theory of muscular 

 contraction. 



From the study of individual man it is but a step to the consideration 

 of him in his social relation, and this, accordingly, had been done in the 

 second part of my work on Physiology. But the subject being too ex- 

 tensive to be dealt with satisfactorily in that manner, I published the 



