On the other hand, there are men who, after having become thoroughly and experimentally acquainted with the nature of dyes, have not been able to reconcile their observations with the received theory; who have, in short, discovered its weak points, and sought for a general view more consonant to nature and experience. When we come to the names of Castel and Gülich, in our historical review, we shall have occasion to enter into this more fully, and an opportunity will then present itself to show that an assiduous experience in taking advantage of every accident may, in fact, be said almost to exhaust the knowledge of the province to which it is confined. The high and complete result is then submitted to the theorist, who, if he examines facts with accuracy, and reasons with candour, will find such materials eminently useful as a basis for his conclusions.--Note A A. RELATION TO PHYSIOLOGY AND PATHOLOGY. 733. If the phenomena adduced in the chapter where colours were considered in a physiological and pathological view are for the most part generally known, still some new views, mixed up with them, will not be unacceptable to the physiologist. We especially hope to have given him cause to be satisfied by classing certain phenomena which stood alone, under analogous facts, and thus, in some measure, to have prepared the way for his further investigations. 734. The appendix on pathological colours, again, is admitted to be scanty and unconnected. We reflect, however, that Germany can boast of men who are not only highly experienced in this department, but are likewise so distinguished for general cultivation, that it can cost them but little to revise this portion, to complete what has been sketched, and at the same time to connect it with the higher facts of organisation. RELATION TO NATURAL HISTORY. 735. If we may at all hope that natural history will gradually be modified by the principle of deducing the ordinary appearances of nature from higher phenomena, the author believes he may have given some hints and introductory views bearing on this object also. As colour, in its infinite variety, exhibits itself on the surface of living beings, it becomes an important part of the outward indications, by means of which we can discover what passes underneath. 736. In one point of view it is certainly not to be too much relied on, on account of its indefinite and mutable nature; yet even this mutability, inasmuch as it exhibits itself as a constant quality, again becomes a criterion of a mutable vitality; and the author wishes nothing more than that time may be granted him to develop the results of his observations on this subject more fully; here they would not be in their place. RELATION TO GENERAL PHYSICS. 737.